Novel targets in the treatment of advanced gastric cancer: a perspective review

Abstract

Gastric cancer is responsible for a high burden of disease globally. Although more extensive use of chemotherapy together with the recent introduction of the two targeted agents trastuzumab and ramucirumab have contributed to marginal outcome prolongation, overall survival for patients with advanced stage disease remains poor. Over the last decade, a number of novel agents have been examined in clinical trials with largely disappointing results. Potential explanations for this are the absence of molecularly selected trial populations or weak predictive biomarkers within the context of a highly heterogeneous disease. In the recently published gastric cancer The Cancer Genome Atlas (TCGA) project a new classification of four different tumour subtypes according to different molecular characteristics has been proposed. With some overlap, several relatively distinct and potentially targetable pathways have been identified for each subtype. In this perspective review we match recent trial results with the subtypes described in the gastric cancer TCGA aiming to highlight data regarding novel agents under evaluation and to discuss whether this publication might provide a framework for future drug development.

Keywords

chromosomal instability clinical trials Epstein Barr virus gastric cancer gastroesophageal cancer genomically stable microsatellite instability molecular profiling The Cancer Genome Atlas

Introduction

Gastric cancer (GC) is responsible for a high global burden of disease; it is the fifth most common cancer worldwide with 951,000 new cases annually, and is the third leading cause of cancer death with 723,000 events every year [Ferlay et al. 2015]. The highest incidence rates occur in Asia; whereas eastern Asia, central and eastern Europe and South America all have high GC-related mortality rates.

Approximately 50% of patients are diagnosed with GC when the disease is already locally advanced or metastatic. For early stage adenocarcinoma surgery remains the only potentially curative treatment, however more than 50% of patients experience disease relapse [Cunningham et al. 2006; Ychou et al. 2011]. Overall survival (OS) of patients with stage IV disease remains poor, between 3 months in the absence of any active treatment and 9–16 months in fit patients within the context of clinical trials [Cunningham et al. 2008; Bang et al. 2010; Wagner et al. 2010].

Treatment of advanced GC: cytotoxic chemotherapy as standard

Chemotherapy remains the backbone of treatment for advanced GC resulting in superior survival outcomes and symptom control and consequently improved quality of life compared with best supportive care [Wagner et al. 2010]. The chemotherapy regimen of choice varies geographically, however a platinum fluoropyrimidine based treatment is accepted worldwide as first-line therapy. In the UK NCRI REAL-2 clinical trial, oxaliplatin demonstrated noninferiority to cisplatin and capecitabine to infused 5-fluorouracil. Based on this study, a triplet regimen consisting of epirubicin, a platinum salt (cisplatin or oxaliplatin) and a fluoropyrimidine (capecitabine or 5-fluorouracil) is a standard first-line option for fit patients and results in a median OS between 9 and 11 months [Cunningham et al. 2008]. Similar survival outcomes have been achieved by adding docetaxel to the doublet cisplatin and 5-fluorouracil, although this regimen is associated with significantly increased toxicity [Van Cutsem et al. 2006]. Doublet regimens consisting of cisplatin or oxaliplatin and a fluoropyrimidine are a validated option for patients not fit for three drugs. For patients who are not suitable for platinum, irinotecan-containing regimens may provide a reasonable alternative [Guimbaud et al. 2014].

Following publication of the ToGA trial, the use of the monoclonal antibody trastuzumab targeting the human epidermal growth factor receptor 2 (HER2) in combination with cisplatin and fluorouracil has become a standard treatment for HER-2 positive GC (approximately 20% of patients in total) [Bang et al. 2010]. The role of second-line treatment with a taxane or irinotecan has recently also been accepted globally, as several trials have demonstrated a marginal (approximately 6 weeks) benefit in survival and quality of life [Thuss-Patience et al. 2011; Kang et al. 2012; Fuchs et al. 2014; Ford et al. 2014]. The antiangiogenic monoclonal antibody ramucirumab has recently been approved as a single agent or in combination with paclitaxel as second-line therapy, and for appropriate patients may increase OS in this setting to over 9 months when delivered in combination with paclitaxel [Fuchs et al. 2014; Wilke et al. 2014]. Thus it is clear that with the notable exception of trastuzumab, the introduction of molecularly targeted novel agents into clinical practice has lagged behind other cancers. Given the low median survival time for patients with metastatic GC, further research is required in this area.

The results of the recently published The Cancer Genome Atlas (TCGA) for GC have highlighted the complex heterogeneity of this disease [The Cancer Genome Atlas Research Network, 2014]. Using these results as a guide, in this perspective review we aim to identify and discuss data regarding novel agents directed to the targets which characterise each molecular GC subtype. In doing so, we will examine how the TCGA results provide a context to discuss previous trials in GC, and may also provide a framework for future drug development.

Molecular characterization from the TCGA analysis

Several previous GC classification systems have been described, however the generalizability of these was questionable due to the geographically discrete patient groups used and failure to validate results in external datasets [Shah et al. 2011; Tan et al. 2011; Deng et al. 2012; Lei et al. 2013; Smyth et al. 2013]. In order to overcome these challenges for the GC TCGA project, a total of 295 untreated surgically resected gastric adenocarcinomas were evaluated from a global population. Six distinct methodologies [array-based somatic copy number analysis, whole-exome sequencing, array-based DNA methylation profiling, messenger RNA sequencing, microRNA (miRNA) sequencing and reverse-phase protein array] were used to characterize patients, plus evaluation of microsatellite instability. The authors proposed a new classification in four different subtypes according to shared molecular characteristics. These were Epstein Barr positive tumours (EBV), microsatellite unstable tumours (MSI), genomically stable tumours (GS) and tumours with chromosomal instability (CIN). Although some characteristics of each subtype partially overlap, the prevalence of relatively distinct potentially targetable pathways has been identified for each subgroup (see Table 1).

Table 1.

Characteristics of the four diverse molecular subtypes (modified from TCGA report; total number: 295).

Characteristics		EBV (9%)	MSI (22%)	CIN (50%)	GS (20%)
Sex	Female	5 (19%)	36 (56%)	50 (34%)	22 (38%)
	Male	21 (81%)	28 (44%)	97 (66%)	36 (62%)
Lauren classification	Diffuse	5 (19%)	6 (9%)	18 (12%)	40 (69%)
	Intestinal	15 (57%)	48 (75%)	118 (80%)	15 (26%)
	Mixed	3 (11%)	3 (5%)	10 (7%)	3 (5%)
	not reported	3 (11%)	7 (11%)	1 (1%)	0
Main actionable targets		PD-L1/2 expressionJAK2 expressionPIK3CA mutation	Loss of HLA class 1 complexesPIK3CA mutation	HER2 amplificationEGFR amplificationMET amplificationCCNE1, CCND1, CDK6 amplificationVEGFA amplificationFGFR2 amplification	VEGFA amplificationFGFR2 amplificationCell adhesion pathwaysRHO-A?

CCND1, cyclin D1; CCNE1, cyclin E1; CDK, cyclin dependent kinase; CIN, chromosomal instability; EBV, Epstein Barr virus; EGFR, epidermal growth factor receptor; FGFR, fibroblast growth factor receptor; GS, genomically stable; HER2, epidermal growth factor receptor 2; HLA, human leukocyte antigen; JAK, Janus kinase; MSI, microsatellite unstable; OGJ, oesophagogastric junction; PD-L, programmed death ligand; PIK3CA, phosphatidylinositol 4,5 bisphosphate 3 kinase, catalytic subunit α; MET: mesenchimal epithelial transition; VEGFA, vascular endothelial growth factor A.

Targetable pathways in EBV tumours: immune-based therapies, phosphatidylinositol 4,5 bisphosphate 3 kinase, catalytic subunit α and Janus kinase 2

The EBV subtype (9% tumours in TCGA) is characterized by high EBV burden (determined using mRNA, miRNA, exome and whole genome sequencing) and high levels of DNA promoter hypermethylation (all EBV-positive tumours demonstrated CDKN2A promoter methylation). EBV-positive tumours were more frequently located in the gastric fundus or body and 81% of cases occurred in men. Relevant targetable pathways identified in this subtype were related to the elevated expression of programmed death ligand 1 and 2 (PD-L1 and PD-L2), Janus kinase 2 (JAK2) amplification and phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit α (PIK3CA) mutation.

An increasing enthusiasm for immunotherapy agents has been rapidly propagated from the treatment of advanced melanoma to several tumour types, including GC [Robert et al. 2011; Wolchok et al. 2013; Larkin et al. 2015]. Pembrolizumab, a highly selective immunoglobulin G4k humanized monoclonal antibody targeting the PD-1 receptor demonstrated activity in the phase Ib KEYNOTE-012 trial in a cohort of heavily pretreated Asian and non-Asian patients with GC, with acceptable toxicity profile [Shankaran et al. 2015]. On central review, overall response rate was 22% [95% confidence interval (CI) 10–39%] with median duration of response of 24 weeks (range 8–33 weeks). As most responses to chemotherapy in GC are short lived, this is of significant interest. A correlation between PD-L1 expression (defined as PD-L1 ⩾ 1% on archival tissue) and response has been subsequently demonstrated [Bang et al. 2015b]. A double checkpoint inhibition strategy targeting both the PD-1/PD-L1 and CTLA-4/B7 interaction which has already demonstrated efficacy in patients with melanoma is under evaluation in several GC trials such as nivolumab + ipilimumab [ClinicalTrials.gov identifier: NCI01928394] and MEDI4734 and tremelimumab [ClinicalTrials.gov identifier: NCI02340975].

The JAK pathway has to date been primarily a targeted strategy for myeloproliferative and inflammatory disorders and has only recently extended to solid tumours [Buchert et al. 2015]. With respect to gastrointestinal malignancies, ruxolitinib, a JAK1 and JAK2 inhibitor, has demonstrated preliminary efficacy in combination with capecitabine in pancreatic adenocarcinoma and is currently under evaluation in colorectal cancer in combination with regorafenib [ClinicalTrials.gov identifier: NCI02119676] [Hurwitz et al. 2014]. To our knowledge there are no trials ongoing in GC.

Activating mutations of the PIK3CA gene represent a further potentially actionable target in GC. In previous series the prevalence of this mutation has been reported to range between 5% and 16% [Barbi et al. 2010] and to be more frequent in white patients compared with Asian patients (15% versus 7%) [Chong et al. 2014]. In the TCGA report, 80% of EBV tumours and 42% of MSI tumours harboured a mutation in PIK3CA (although more commonly in the exon 20 kinase domain in non-EBV type tumours), thus supporting the rationale of pursuing the inhibition of this pathway in clinical trials.

Alternative mechanisms of targeting the PI3K pathway in cancer include inhibiting downstream effectors such as mechanistic target of rapamycin (mTOR) and AKT. Despite initially promising results with a disease control rate of over 50% in a phase II study, the oral mTOR inhibitor everolimus failed to improve survival compared with placebo in a phase III multicentre randomized clinical trial in patients with previously treated advanced GC, although a trend toward a reduced risk of death in non-Asian patients was noted [Ohtsu et al. 2013]. This trial was not biomarker selected and translational analyses are awaited. Several AKT inhibitors are currently being examined in GC: a randomized phase II trial of ipatasertib or placebo in combination with mFOLFOX (chemotherapy regimen for treatment of colorectal cancer, made up of the drugs: FOL – Folinic acid (leucovorin) F – Fluorouracil (5-FU) OX – Oxaliplatin (Eloxatin)) as first-line treatment for advanced GC recently completed recruitment while afuresertib in combination with paclitaxel in a second-line setting is currently under investigation in a phase IB study in an unselected population [ClinicalTrials.gov identifier: NCT01896531, NCT02240212]. In a molecularly selected population a further orally available AKT inhibitor, AZD5363, is currently being utilized in combination with paclitaxel in a second-line setting in patients with GC harbouring PIK3CA mutation or amplification [ClinicalTrials.gov identifier: NCT02451959].

Targetable pathways in MSI tumours

The MSI-high subtype represented 22% of the samples of the TCGA analysis and was characterized by elevated mutation rates and hypermethylation resulting in MutL homolog 1 (MLH1) silencing. This population was older, with a median age of 72 years and with a higher proportion of female patients (56%) compared with the other subtypes. Major histocompatibility complex class I gene alterations were common in this subtype. This, together with the increased number of tumour-specific neoantigens derived from hypermutated genes, suggest a potential additional role for immunotherapy for this category of tumour. Evidence of activity of pembrolizumab in a subset of patients with MSI-positive colorectal cancer has recently been presented; immune-related objective response and progression free survival rates were 40% and 78% respectively [Le et al. 2015]. With respect to the data presented on pembrolizumab in GC to date, neither MSI nor EBV status has been revealed at the time of writing. In addition to mutations in the kinase domain of PIK3CA, mutations in ERBB3 and KRAS among others were found in significant numbers in MSI tumours, which may represent other potential targetable abnormalities for future drug development.

One potential challenge in developing suitable candidate therapies for patients with MSI- and EBV-type tumours is that, paradoxically, these patients are likely to have improved survival following surgery compared with patients with other subtypes. Both MSI and EBV positivity have been validated as favourable prognostic factors in resected GC, and therefore may be present in lower proportions in the metastatic setting, with subsequent case finding difficulty hindering trial design [Camargo et al. 2014; Choi et al. 2014].

Targetable pathways in CIN tumours: receptor tyrosine kinase amplifications predominate

The largest subgroup within the gastric TCGA is that of chromosomally unstable tumours, comprising half of all patients (65% of junctional tumours) and correlating well with an intestinal pathological phenotype. Within this group, several targetable pathways have been identified, the majority of them related to receptor tyrosine kinase (RTK) gene amplifications, including HER2, epidermal growth factor receptor (EGFR), mesenchymal epithelial transition factor (MET), fibroblast growth factor receptor (FGFR) and vascular endothelial growth factor A (VEGFA). This group of cancers has been the subject of extensive clinical trials over the past decade.

The HER2 pathway has been well described in GC and trastuzumab is the sole validated targeted therapy in this disease [Bang et al. 2010] (see Table 2). Following ToGA, several anti-HER2 agents have been examined. The addition of pertuzumab (a monoclonal antibody blocking HER2/HER3 dimerization) to trastuzumab and docetaxel has already demonstrated a survival benefit in patients with breast cancer [Baselga et al. 2012]. To evaluate this combination in GC, a phase III multicentre international clinical trial of pertuzumab or placebo in combination with trastuzumab and cisplatin–fluoropyrimidine regimen is ongoing, with an estimated study completion date of September 2021 [ClinicalTrials.gov identifier: NCT01774786].

Table 2.

Key randomized phase III trial with targeted agents in previously untreated gastric cancer.

Trial name	Selected biomarker	Treatment	Number of patients	Primary endpoint	Hazard ratio (95% confidence interval)	p value	Median OS (months)
ToGA[Bang et al. 2010]	HER2 expression/amplification	CF/CXCF/CX +trastuzumab	290294	OS	0.74 (0.60–0.91)	0.004	13.811.1
LOGiC[Hecht et al. 2013]	HER2 expression/amplification	CapeOXCapeOx+lapatinib	273272	OS	0.91 (0.73–1.12)	0.35	10.512.2
REAL-3	all comers	EOX	275	OS	1.37 (1.07–1.76)	0.013	11.3
[Waddell et al. 2013]		EOX+panitumumab	278				8.8
EXPAND	all comers	CX	449	PFS	1.09 (0.92–1.29)	0.32	10.7
[Lordick et al. 2013]		CX+cetuximab	445				9.4
RILOMET[Cunningham et al. 2015]	MET positive by IHC HER2 negative	ECXECX+rilotumumab	305304	OS	1.37 (1.06–1.78)	0.016	11.5 9.6
AVAGAST	all comers	CX	387	OS	0.87 (0.73–1.03)	0.1	10.1
[Ohtsu et al. 2011]		CX+bevacizumab	387				12.1
AVATAR	all comers	CX	102	OS	1.11 (0.79–1.56)	0.5567	11.4
[Shen et al. 2015]		CX+bevacizumab	100				10.5

CapeOX, capecitabine, oxaliplatin; CF, cisplatin, fluorouracil; CX, cisplatin, capecitabine; ECX, epirubicin, cisplatin and capecitabine; EOX, epirubicine, oxaliplatin, capecitabine; HER2, human epidermal growth factor receptor 2; IHC, immunohistochemistry; OS, overall surivial; PFS, progression-free survival.

At this time, standard salvage treatment options for HER2-positive tumours are similar to those for HER2-negative disease, however the blockade of the HER2 pathway beyond trastuzumab progression is under investigation. The antibody–drug conjugate trastuzumab emtansine (T-DM1) has been evaluated in the second-line setting in a phase II clinical trial in previously treated patients with HER2-positive metastatic or advanced GC compared with docetaxel or paclitaxel. The primary objective of the study is OS and the results are anticipated in 2016 [ClinicalTrials.gov identifier: NCT01641939]. MM-111, a bispecific antibody fusion protein binding both HER2 and HER3 (the preferred dimerization partner of HER2) has been evaluated in a phase II clinical trial in combination with trastuzumab and paclitaxel [ClinicalTrials.gov identifier: NCT01774851], however this trial was terminated following inferior progression-free survival (PFS) results in the experimental arm.

Straddling the border between HER2 and EGFR inhibition, lapatinib, a dual inhibitor of EGFR and HER2, has been examined first line in combination with capecitabine and oxaliplatin and second line in combination with paclitaxel [Hecht et al. 2013; Satoh et al. 2014b]. Both phase III studies failed to meet their primary endpoint. In the TRIO013/LOGiC Trial, the primary endpoint of OS in patients with centrally confirmed harbouring HER2 amplification by fluorescence in situ hybridization (FISH) was not met [hazard ratio (HR) 0.91, 95% CI 0.73–1.12, p = 0.35]. However, a subgroup analysis demonstrated significant benefit in Asian patients and those younger than 60 years [Hecht et al. 2013]. Similarly, in the TyTAN trial, patients with previously treated HER2 FISH amplified tumours were randomized to paclitaxel + lapatinib/placebo. No significant benefit in OS was seen (HR 0.84, 95% CI 0.64–1.11, p = 0.1044). However, a significant benefit in response rate in patients with FISH amplification and 3+ immunohistochemistry (IHC) was noted [Satoh et al. 2014b]. Although the primary endpoint was not met in either study, subgroup analysis has provided proof of concept for some activity of lapatinib in HER2-amplified cancers. Investment in dual inhibitors of the ERBB family continues; at the recent American Society of Medical Oncology (ASCO) Annual Meeting 2015 an oral reversible tyrosine kinase inhibitor of the EGFR and HER2 named S-222611 demonstrated a 15% response rate (including one complete response) in HER2-positive GC [Deva et al. 2015].

EGFR gene amplification is the second most frequent RTK alteration reported in the GC TCGA study and is demonstrated in 10% of CIN subtype tumours. This finding was consistent with previous data, with rates between 4.9% and 7.7% being reported [Deng et al. 2012; Kiyose et al. 2012]. Unfortunately, disappointing results from two large randomized phase III trials have discouraged further investigation of anti-EGFR agents in molecularly unselected populations [Lordick et al. 2013; Waddell et al. 2013]. Panitumumab added to epirubicin, capecitabine and oxaliplatin as first-line treatment for metastatic or locally advanced oesophagogastric adenocarcinomas resulted in detrimental outcomes compared with chemotherapy alone [Waddell et al. 2013]. This was hypothesized to be related to a reduction in chemotherapy dose intensity due to overlapping toxicity (in terms of grade 3–4 diarrhoea), and potentially negative interactions between anti-EGFR agents and oxaliplatin-based regimens. Two other anti-EGFR agents, cetuximab and nimotuzumab, did not demonstrate benefit when added to standard chemotherapy. Cetuximab did not result in a survival advantage when added to the cisplatin–capecitabine regimen in previously untreated advanced junctional or gastric adenocarcinoma in the EXPAND trial [Lordick et al. 2013] and in two phase II randomized studies nimotuzumab failed to demonstrate benefit both in the first-line setting in combination with cisplatin and S-1, and in the second-line setting with irinotecan (even in a subset expressing EGFR 2+ or 3+ by IHC) [Satoh et al. 2014a; Du et al. 2015]. Additionally, two anti-EGFR tyrosine kinase inhibitors erlotinib and gefitinib were ineffective in a phase II trial and phase III trial compared with best supportive care in oesophageal and junctional cancers [Dragovich et al. 2006; Dutton et al. 2014]. However, intriguing retrospective biomarker analyses of the COG trial suggest that a subpopulation of tumours with EGFR copy number gain may benefit from anti-EGFR therapy, implying that refining the EGFR biomarker may yet yield positive results [Petty et al. 2014].

Disappointingly, both monoclonal antibodies and RTK inhibitors targeting the MET pathway have failed to meet expectations [Cunningham et al. 2015; Shah et al. 2015]. High variability of MET protein expression by IHC has been reported in case series, ranging from 22% to 90% [Ha et al. 2013; Scagliotti et al. 2013], whereas MET amplification has been more homogeneously reported in the literature as between 2% and 10% and confirmed in 8% of CIN subtype tumours in the TCGA series [Peng et al. 2014; The Cancer Genome Atlas Research Network, 2014]. Both MET overexpression and MET amplification have been validated as negative prognostic factors in GC and this pathway was therefore promising for pharmacological intervention [Peng et al. 2014].

Rilotumumab, a fully human monoclonal antibody targeting the hepatocyte growth factor (HGF), ligand of MET receptor, was associated with significantly longer PFS and OS when added to epirubicin, cisplatin and capecitabine chemotherapy in treatment naïve molecularly unselected patients with advanced gastric or oesophagogastric junction tumours in a multicentre phase II trial [Iveson et al. 2014]. For patients with MET-positive tumours, OS was longer in rilotumumab-treated patients compared with those on placebo (10.6 versus 5.7 months respectively). However, the randomized phase III trial recently presented by Cunningham and colleagues in patients with MET-positive tumours by IHC was terminated prematurely due to an imbalanced number of deaths in the experimental arm [Cunningham et al. 2015]. Concurrently, disappointing results were also presented regarding another anti-MET antibody, onartuzumab, in combination with mFOLFOX [Shah et al. 2015]. Compared with placebo in previously untreated HER2-negative advanced oesophagogastric adenocarcinomas in a randomized phase II study, onartuzumab did not improve the primary endpoint of PFS in an unselected population or in the MET-positive subgroup. The orally available MET kinase inhibitor AMG337 demonstrated encouraging preliminary activity in patients with oesophagogastric adenocarcinomas after failure of first-line treatment; of 10 patients with MET-amplified tumours, one patient had complete response, four had partial response and two had stable disease. However, in March 2015 after a prespecified interim review of efficacy and safety data, the study was terminated [Kwak et al. 2015].

In the GC TCGA dataset, 9% and 8% of CIN tumours and GS tumours respectively harboured amplification of the FGFR2 gene [The Cancer Genome Atlas Research Network, 2014]. Several orally available pan-FGFR inhibitors are under investigation in GC and other tumour subtypes. The results of a phase II randomized trial of AZD4547 (a selective inhibitor of FGFR1, 2 and 3) or paclitaxel in patients with FGFR2 amplification or polysomy in a second-line setting have recently been presented [Bang et al. 2015c]. In the population screened, the prevalence of FGFR2 amplification (9%) was in line with TCGA data. Following an interim analysis, in which PFS was no different between the experimental and paclitaxel groups, the study was halted prematurely. Biomarker analysis from the study has underlined high intratumour heterogeneity of FGFR2 amplification, an issue which has also been problematic in HER2 assessment in GC [Kim et al. 2011]. Interestingly, concurrently with this study a further phase II study with the same compound and the same target population identified high a FISH ratio (>8) and the presence of elevated FGFR2 copy number in free plasma DNA as potential biomarkers predictive of response to AZD4547, highlighting that thorough evaluation and refinement of the biomarker is a requisite for informed drug development [Smyth et al. 2015]. Two ongoing phase II studies are evaluating dovitinib (a multikinase inhibitor targeting FGFR) after failure of first-line treatment as a single agent in FGFR2-amplified GC (defined as copy number >3) or in combination with docetaxel in a biomarker unselected population [ClinicalTrials.gov identifier: NCT01719549, NCT01921673].

On a broader level the chromosomal instability which is characteristic of CIN subset GC may be exploited for therapeutic gain. Defects in DNA damage repair lead not only to point mutations but also to loss of part or whole chromosomes [Watkins et al. 2014; Marquard et al. 2015]. The presence of such genomic scars is associated with platinum sensitivity, and also sensitivity to poly ADP ribose polymerase (PARP) inhibitors. In ovarian cancer, the presence of large-scale homologous DNA repair defects (and not only BRCA mutations) has been associated with an increased benefit from PARP inhibition using rucaparib [McNeish et al. 2015; Shapira-Frommer et al. 2015]. As a randomized phase II trial of olaparib in combination with paclitaxel demonstrated an overall survival benefit in a nonbiomarker-selected second-line GC population, it will be interesting to observe whether molecular selection of patients using an HRD-LOH (Homologous Recombination Deficiency-Loss of Heterozygosity) signature or other measure of chromosomal instability will yield further incremental gains [Bang et al. 2015b].

Unique targetable pathways in GS tumours: RHOA

Tumours which did not meet the criteria for the previously discussed three subtypes, which are EBV negative, mismatch repair proficient and with low degree of aneuploidy, were classified as GS [The Cancer Genome Atlas Research Network, 2014]. This subtype represented 20% of the TCGA samples and has been associated with diffuse histology, earlier age at presentation (median 59 years) and distal localization. Several unique subtype specific molecular changes have been described for GS tumours. These include abnormalities of RHOA signalling encompassing mutations and CLDN18–ARHGAP26 fusions (approximately 15% for each aberration in a mutually exclusive fashion) which have been validated in external datasets [Kakiuchi et al. 2014; Yao et al. 2015]. As Ras homolog gene family, member A (RHOA) signalling has a role in cell motility, these changes may account for the discohesive, invasive nature of this GC subtype. Although not currently targetable, these pathways represent a valuable signpost for development of effective treatments for diffuse GC.

With respect to pathways currently under investigation in clinical trials, in common with the CIN subtype, the presence of FGFR2 and VEGFA amplification in GS tumours suggests angiogenesis an attractive targetable pathway. These amplifications also provide an important potential lesson regarding interpretation of the TCGA; although some pathways are quite unique to specific subtypes (RHOA dysregulation is an excellent example), others such as PIK3CA mutations and receptor tyrosine kinase amplifications are common to more than one subtype. For this reason, care is required when selecting patients for clinical trials so they are not excluded based on subtype alone: instead the underlying molecular aberration should be characterized.

Targets outside the TCGA subtypes: angiogenesis

The TCGA represents a new paradigm for the classification of GCs. However, it is not definitive and there are several potentially exploitable molecular targets which are not explicit components of this classification system. The most prominent of these is angiogenesis. As increased expression of angiogenic markers such as VEGF is associated with aggressive disease biology and inferior survival in patients with GC, angiogenesis is an attractive therapeutic target in this disease [Maeda et al. 1996; Song et al. 2002; Lieto et al. 2008]. However, despite significant survival benefits in other cancers when bevacizumab (a monoclonal antibody targeting VEGF) was added to standard first-line treatment in two large multicentre randomized phase III trials in GC, it failed to improve survival [Ohtsu et al. 2011; Shen et al. 2015]. The population in both studies was biomarker unselected; however the AVAGAST translational programme identified a survival benefit in patients with higher expression of VEGFA and low neuropilin 1 expression treated in the experimental arm in non-Asian regions [Van Cutsem et al. 2012].

As previously discussed, ramucirumab (a fully humanized monoclonal antibody targeting VEGFR2) recently became the second targeted agent approved for the treatment of GC. Ramucirumab has demonstrated significant benefit in OS, PFS and disease control rate as a single agent compared with placebo in the REGARD trial and in combination with paclitaxel compared with paclitaxel alone in the RAINBOW trial [Fuchs et al. 2014; Wilke et al. 2014] (see Table 3). However, the same success was not apparent when employed in a first-line setting in combination with mFOLFOX, suggesting a potential negative interaction with oxaliplatin-based regimens (or synergy with taxanes) [Yoon et al. 2014]. A further phase III randomized trial of ramucirumab or placebo in combination with cisplatin and capecitabine in a first-line setting in HER2-negative GC has recently commenced [ClinicalTrials.gov identifier: NCT02314117].

Table 3.

Key randomized phase III trial with targeted agents as salvage treatment for gastric cancer.

Trial name	Selected biomarker	Treatment	Number of patients	Primary endpoint	Hazard ratio (95% confidence interval)	p value	Median OS (months)
TyTAN[Satoh et al. 2014b]	HER2 amplification by FISH	PaclitaxelPaclitaxel+lapatinib	129132	OS	0.84 (0.64–1.1)	0.1044	8.911
REGARD[Fuchs et al. 2014]	All comers	BSCBSC+ramucirumab	117238	OS	0.776 (0.603–0.998)	0.047	3.85.2
RAINBOW[Wilke et al. 2014]	All comers	PaclitaxelPaclitaxel+ramucirumab	335330	OS	0.807 (0.678–0.962)	0.017	7.49.6
NCT01512745[Li et al. 2014]	All comers	PlaceboApatinib	92181	OS	0.71 (0.54–0.94)	0.016	4.66.4
GRANITE[Ohtsu et al. 2013]	All comers	BSCBSC+everolimus	217439	OS	0.90 (0.75–1.08)	0.124	4.35.4

BSC, best supportive care; FISH, fluorescence in situ hybridization; HER2, human epidermal growth factor receptor 2; OS, overall survival.

Apatinib (a RTK targeting VEGFR2) was associated with significant survival prolongation compared with placebo (140 versus 195 days, HR 0.71, p < 0.016) in a chemorefractory Chinese population, providing further evidence in supporting VEGFR2 as a valuable target in GC [Li et al. 2013]. However, as development of targeted therapy in GC has been hampered by regional differences in efficacy, it is unknown if these results would be replicated outside Asia. Another multikinase inhibitor targeting VEGFR2 and tyrosine kinase with Ig and EGF (epidermal growth factor) homology domains (TIE2) (regorafenib) has recently demonstrated a significant improvement in PFS compared with placebo (11.1 versus 3.9 weeks, HR 0.40, p < 0.0001) in patients with refractory advanced oesophago GC treated in an international phase II trial [Pavlakis et al. 2015]. Whether the efficacy demonstrated in any of the above trials of antiangiogenic therapy is related to the significant proportion of patients with VEGFA amplification is unknown, however as the other RTK amplifications do appear to confer sensitivity to target inhibition, this may well be true.

Alternatives to the GC TCGA classification system

A recent landmark publication from the Asian Cancer Research Group describing an alternative classification system to the GC TCGA has been thought provoking [Cristescu et al. 2015]. Using gene expression data on 300 Korean GC specimens, four distinct classes of tumour were identified and validated in two independent datasets. The four subgroups defined were MSI (23%), mesenchymal (15%) and microsatellite stable (MSS) p53 (26%) active and inactive (36%) tumours. Although the molecular characterization of this dataset lacks the complexity of the TCGA, it benefits from significantly longer follow up, and this classifier was prognostic and associated with distinct patterns of recurrence. In common with the GC TCGA, the presence of distinct molecular drivers is enriched in separate subgroups (e.g. HER2 amplification in MSS p53 inactive), however there were also differences in the proportion of clinical phenotypes between the two datasets (e.g. diffuse GC 45% Asian Cancer Research Group (ACRG) versus 24% TCGA)which are likely to have a knock on effect on the prevalence of underlying driver mutations or copy number alterations. As the TCGA dataset was derived from a global rather than an Asian dataset, it is used as the basis for this perspective review, however the ACRG classifier may also have significant clinical relevance.

Conclusion

GC remains a highly lethal disease worldwide. Although a large number of new drugs have been investigated, trastuzumab and ramucirumab are the only two targeted agents currently approved for the treatment of advanced disease. One of the many reasons to explain the lack of efficacy of targeted agents in large trials is the absence of biomarker-driven trials or indeed the methodology of biomarker selection. The recent analysis of the GC TCGA project has highlighted the variability of this disease with respect to underlying molecular drivers which is further complicated by intra-patient heterogeneity of biomarker expression [Kim et al. 2011; Smyth et al. 2015]. Although liquid biopsies could represent a possible solution to this complex matter, large-scale results of translational programmes in this field are required before implementing such practice changes.

The large amounts of data derived from molecular characterization panels are hypothesis generating; how to integrate them into clinical practice remains challenging. In this review, we matched clinical trial data reported in the recent literature with the different pathways highlighted in the four molecular subtypes identified by the TCGA analysis. We acknowledge that this is a somewhat artificial approach, as these subtypes do not at the current time define clinical practice or drug development. However, they may aid in the design of future clinical trials aiming to personalize treatment in several ways. First, by helping to identify the driving pathways sustaining tumour growth. Second, by identifying potential combination treatments targeting pathways with nonoverlapping toxicities. And third, by identifying predictable mechanisms of resistance with a view to designing sequential strategies.

A key caveat here is that as targetable molecular characteristics are enriched rather than invariably present in each subtype (with the exception of MSI), knowledge of the subtype alone may be insufficient to allocate a patient to a clinical trial. Instead and still usefully, it may identify a smaller population in which to screen for protocol eligible molecular aberrations. It is also crucial to remind ourselves that the functional implications of each genetic alteration may be context dependent, as demonstrated by the distinct pattern of the oncogenic effect of BRAF mutation in colorectal cancer and melanoma; preclinical validation of the effects of oncogenic driver aberrations may be useful prior to embarking on ambitious clinical trial programmes. Furthermore, these assumptions are made based on the translation of TCGA results into a simple molecular profile which is adapted to routine clinical use and this necessary work has not yet been completed. Finally, with the emergence of ever more refined patient groups, adaptive design and umbrella clinical trials will be required to develop personalized treatments in this highly heterogeneous disease.

Footnotes

Funding

EF and ES acknowledge the support of the NIHR ICR/RMH BRC.

Conflict of interest statement

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

References

Bang

Chung

Shankaran

Geva

Catenacci

Gupta

. (2015a) Relationship between PD-L1 expression and clinical outcomes in patients with advanced gastric cancer treated with the anti-PD-1 monoclonal antibody pembrolizumab (MK-3475) in KEYNOTE-012. J Clin Oncol 33: 4001.

Bang

Lee

Cho

Song

Lee

. (2015b) Randomized, double-blind phase II trial with prospective classification by ATM protein level to evaluate the efficacy and tolerability of olaparib plus paclitaxel in patients with recurrent or metastatic gastric cancer. J Clin Oncol. Epub ahead of print 17 August 2015. DOI: 10.1200/JCO.2014.60.0320.

Bang

Van Cutsem

Feyereislova

Chung

Shen

Sawaki

. (2010) Trastuzumab in combination with chemotherapy versus chemotherapy alone for treatment of HER2-positive advanced gastric or gastro-oesophageal junction cancer (ToGA): a phase 3, open-label, randomised controlled trial. Lancet 376: 687–697.

Bang

Van Cutsem

Mansoor

Petty

Chao

Cunningham

. (2015c) A randomized, open-label phase II study of AZD4547 (AZD) versus paclitaxel (P) in previously treated patients with advanced gastric cancer (AGC) with fibroblast Growth Factor Receptor 2 (FGFR2) polysomy or gene amplification (amp): SHINE study. J Clin Oncol 33: 4014.

Barbi

Cataldo

De Manzoni

Bersani

Lamba

Mattuzzi

. (2010) The analysis of PIK3CA mutations in gastric carcinoma and metanalysis of literature suggest that exon-selectivity is a signature of cancer type. J Exp Clin Cancer Res 29: 32.

Baselga

Cortés

Kim

Hegg

. (2012) Pertuzumab plus trastuzumab plus docetaxel for metastatic breast cancer. N Engl J Med 366: 109–119.

Buchert

Burns

Ernst

(2015) Targeting JAK kinase in solid tumors: emerging opportunities and challenges. Oncogene. Epub ahead of print 18 May 2015. DOI: 10.1038/onc.2015.150.

Camargo

Kim

Chiaravalli

Kim

Corvalan

Matsuo

. (2014) Improved survival of gastric cancer with tumour Epstein-Barr virus positivity: an international pooled analysis. Gut 63: 236–243.

Choi

Bae

Kwon

Cho

Shin

. (2014) Is microsatellite instability a prognostic marker in gastric cancer? a systematic review with meta-analysis. J Surg Oncol 110: 129–135.

10.

Chong

Loh

Thakkar

Pang

Iacopetta

Soong

(2014) Phosphatidylinositol-3-kinase pathway aberrations in gastric and colorectal cancer: meta-analysis, co-occurrence and ethnic variation. Int J Cancer 134: 1232–1238.

11.

Cristescu

Lee

Nebozhyn

Kim

Ting

Wong

. (2015) Molecular analysis of gastric cancer identifies subtypes associated with distinct clinical outcomes. Nat Med 21: 449–456.

12.

Cunningham

Allum

Stenning

Thompson

Van

Velde

Nicolson

. (2006) Perioperative chemotherapy versus surgery alone for resectable gastroesophageal cancer. N Engl J Med 355: 11–20.

13.

Cunningham

Starling

Rao

Iveson

Nicolson

Coxon

. (2008) Capecitabine and oxaliplatin for advanced esophagogastric cancer. N Engl J Med 358: 36–46.

14.

Cunningham

Tebbutt

Davidenko

Murad

Al-Batran

Ilson

. (2015) Phase III, randomized, double-blind, multicenter, placebo (P)-controlled trial of rilotumumab (R) plus epirubicin, cisplatin and capecitabine (ECX) as first-line therapy in patients (pts) with advanced MET-positive (pos) gastric or gastroesophageal junction (G/GEJ) cancer: RILOMET-1 study. J Clin Oncol 33: 4000.

15.

Deng

Goh

Wang

Das

Tao

Tan

. (2012) A comprehensive survey of genomic alterations in gastric cancer reveals systematic patterns of molecular exclusivity and co-occurrence among distinct therapeutic targets. Gut 61: 673–684.

16.

Deva

Baird

Cresti

Garcia-Corbacho

Hogarth

Frenkel

. (2015) Phase I expansion of S-222611, a reversible inhibitor of EGFR and HER2, in advanced solid tumors, including patients with brain metastases. J Clin Oncol 33(15_suppl): 2511.

17.

Dragovich

Mccoy

Fenoglio-Preiser

Wang

Benedetti

Baker

. (2006) Phase II trial of erlotinib in gastroesophageal junction and gastric adenocarcinomas: SWOG 0127. J Clin Oncol 24: 4922–4927.

18.

Zheng

Shi

Jiang

Yuan

. (2015) S-1 and cisplatin with or without nimotuzumab for patients with untreated unresectable or metastatic gastric cancer: a randomized, open-label phase 2 trial. Medicine 94: e958.

19.

Dutton

Ferry

Blazeby

Abbas

Dahle-Smith

Mansoor

. (2014) Gefitinib for oesophageal cancer progressing after chemotherapy (COG): a phase 3, multicentre, double-blind, placebo-controlled randomised trial. Lancet Oncol 15: 894–904.

20.

Ferlay

Soerjomataram

Dikshit

Eser

Mathers

Rebelo

. (2015) Cancer incidence and mortality worldwide: sources, methods and major patterns in globocan 2012. Int J Cancer 136: E359–E386.

21.

Ford

Marshall

Bridgewater

Janowitz

Coxon

Wadsley

. (2014) Docetaxel versus active symptom control for refractory oesophagogastric adenocarcinoma (COUGAR-02): an open-label, phase 3 randomised controlled trial. Lancet Oncol 15: 78–86.

22.

Fuchs

Tomasek

Yong

Dumitru

Passalacqua

Goswami

. (2014) Ramucirumab monotherapy for previously treated advanced gastric or gastro-oesophageal junction adenocarcinoma (REGARD): an international, randomised, multicentre, placebo-controlled, phase 3 trial. Lancet 383 (9911): 31–39.

23.

Guimbaud

Louvet

Ries

Ychou

Maillard

Andre

. (2014) Prospective, randomized, multicenter, phase III study of fluorouracil, leucovorin, and irinotecan versus epirubicin, cisplatin, and capecitabine in advanced gastric adenocarcinoma: a French intergroup (Federation Francophone De Cancerologie Digestive, Federation Nationale Des Centres De Lutte Contre Le Cancer, and Groupe Cooperateur Multidisciplinaire En Oncologie) study. J Clin Oncol 32: 3520–3526.

24.

Lee

Kang

Ahn

Park

. (2013) MET overexpression assessed by new interpretation method predicts gene amplification and poor survival in advanced gastric carcinomas. Mod Pathol 26: 1632–1641.

25.

Hecht

Bang

Qin

Chung

Park

. (2013) Lapatinib in combination with capecitabine plus oxaliplatin (CapeOx) in HER2 positive advanced or metastatic gastric (A/MGC), esophageal (EAC), or gastroesophageal (GEJ) adenocarcinoma: the logic trial. J Clin Oncol 31: LBA4001.

26.

Hurwitz

Uppal

Wagner

Bendell

Beck

Wade

. (2014) A randomized double-blind phase 2 study of ruxolitinib (RUX) or placebo (PBO) with capecitabine (CAPE) as second-line therapy in patients (pts) with metastatic pancreatic cancer (mPC). J Clin Oncol 32: 4000.

27.

Iveson

Donehower

Davidenko

Tjulandin

Deptala

Harrison

. (2014) Rilotumumab in combination with epirubicin, cisplatin, and capecitabine as first-line treatment for gastric or oesophagogastric junction adenocarcinoma: an open-label, dose de-escalation phase 1b study and a double-blind, randomised phase 2 study. Lancet Oncol 15: 1007–1018.

28.

Kakiuchi

Nishizawa

Ueda

Gotoh

Tanaka

Hayashi

. (2014) Recurrent gain-of-function mutations of RHOA in diffuse-type gastric carcinoma. Nat Genet 46: 583–587.

29.

Kang

Lee

Lim

Park

Kwon

. (2012) Salvage chemotherapy for pretreated gastric cancer: a randomized phase III trial comparing chemotherapy plus best supportive care with best supportive care alone. J Clin Oncol 30: 1513–1518.

30.

Kim

Lee

Yang

Bang

Kim

(2011) Heterogeneous amplification of ERBB2 in primary lesions is responsible for the discordant ERBB2 status of primary and metastatic lesions in gastric carcinoma. Histopathology 59: 822–831.

31.

Kiyose

Nagura

Tao

Igarashi

Yamada

Goto

. (2012) Detection of kinase amplifications in gastric cancer archives using fluorescence in situ hybridization. Pathol Int 62: 477–484.

32.

Kwak

Lorusso

Hamid

Janku

Kittaneh

Catenacci

. (2015) Clinical activity of AMG 337, an oral MET kinase inhibitor, in adult patients (pts) with MET-amplified gastroesophageal junction (GEJ), gastric (G), or esophageal (E) cancer. J Clin Oncol 33: 1.

33.

Larkin

Chiarion-Sileni

Gonzalez

Grob

Cowey

Lao

. (2015) Combined nivolumab and ipilimumab or monotherapy in untreated melanoma. N Engl J Med 373: 23–34.

34.

Uram

Wang

Bartlett

Kemberling

Eyring

. (2015) PD-1 blockade in tumors with mismatch-repair deficiency. N Engl J Med 372: 2509–2520.

35.

Lei

Tan

Das

Deng

Zouridis

Pattison

. (2013) Identification of molecular subtypes of gastric cancer with different responses to PI3-kinase inhibitors and 5-fluorouracil. Gastroenterology 145: 554–565.

36.

Qin

Guo

Xiong

Bai

. (2013) Apatinib for chemotherapy-refractory advanced metastatic gastric cancer: results from a randomized, placebo-controlled, parallel-arm, phase II trial. J Clin Oncol 31: 3219–3225.

37.

Lieto

Ferraraccio

Orditura

Castellano

Mura

Pinto

. (2008) Expression of vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGFR) is an independent prognostic indicator of worse outcome in gastric cancer patients. Ann Surg Oncol 15: 69–79.

38.

Lordick

Kang

Chung

Salman

Bodoky

. (2013) Capecitabine and cisplatin with or without cetuximab for patients with previously untreated advanced gastric cancer (EXPAND): a randomised, open-label phase 3 Trial. Lancet Oncol 14: 490–499.

39.

Maeda

Chung

Ogawa

Takatsuka

Kang

Ogawa

. (1996) Prognostic value of vascular endothelial growth factor expression in gastric carcinoma. Cancer 77: 858–863.

40.

Marquard

Eklund

Joshi

Krzystanek

Favero

Wang

. (2015) Pan-cancer analysis of genomic scar signatures associated with homologous recombination deficiency suggests novel indications for existing cancer drugs. Biomark Res 3: 9.

41.

McNeish

Oza

Coleman

Scott

Konecny

Tinker

. (2015) Results of ARIEL2: a phase 2 trial to prospectively identify ovarian cancer patients likely to respond to rucaparib using tumor genetic analysis. J Clin Oncol 33: 5508.

42.

Ohtsu

Ajani

Bai

Bang

Chung

Pan

. (2013) Everolimus for previously treated advanced gastric cancer: results of the randomized, double-blind, phase III GRANITE-1 study. J Clin Oncol 31: 3935–3943.

43.

Ohtsu

Shah

Van Cutsem

Rha

Sawaki

Park

. (2011) Bevacizumab in combination with chemotherapy as first-line therapy in advanced gastric cancer: a randomized, double-blind, placebo-controlled phase III study. J Clin Oncol 29: 3968–3976.

44.

Pavlakis

Sjoquist

Tsobanis

Martin

Kang

Bang

. (2015) Integrate: a randomized, phase II, double-blind, placebo-controlled study of regorafenib in refractory advanced oesophagogastric cancer (AOGC): a study by the Australasian Gastrointestinal Trials Group (AGITG) – final overall and subgroup results. J Clin Oncol 33: 4003.

45.

Peng

Zhu

Wang

Gao

. (2014) Prognostic significance of MET amplification and expression in gastric cancer: a systematic review with meta-analysis. PLoS One 9: e84502.

46.

Petty

Dahle-Smith

Miedzybrodzka

Dutton

Murray

Stevenson

. (2014) Epidermal growth factor receptor copy number gain (EGFR CNG) and response to gefitinib in esophageal cancer (EC): results of a biomarker analysis of a phase III trial of gefitinib versus placebo (TRANS-COG). J Clin Oncol 32: 4016.

47.

Robert

Thomas

Bondarenko

O’Day

Weber

Garbe

. (2011) Ipilimumab plus dacarbazine for previously untreated metastatic melanoma. N Engl J Med 364: 2517–2526.

48.

Satoh

Lee

Rha

Sasaki

Park

Komatsu

. (2014a) Randomized phase II trial of nimotuzumab plus irinotecan versus irinotecan alone as second-line therapy for patients with advanced gastric cancer. Gastric Cancer 18: 824–832.

49.

Satoh

Chung

Sun

Doi

. (2014b) Lapatinib plus paclitaxel versus paclitaxel alone in the second-line treatment of HER2-amplified advanced gastric cancer in Asian populations: TyTAN-a randomized, phase III study. J Clin Oncol 32: 2039–2049.

50.

Scagliotti

Novello

Von Pawel

(2013) The emerging role of MET/HGF inhibitors in oncology. Cancer Treat Rev 39: 793–801.

51.

Shah

Bang

Lordick

Tabernero

Chen

Hack

. (2015) Metgastric: a phase III study of onartuzumab plus mFOLFOX6 in patients with metastatic HER2-negative (HER2-) and MET-positive (MET+) adenocarcinoma of the stomach or gastroesophageal junction (GEC). J Clin Oncol 33: 4012.

52.

Shah

Khanin

Tang

Janjigian

Klimstra

Gerdes

. (2011) Molecular classification of gastric cancer: a new paradigm. Clin Cancer Res 17: 2693–2701.

53.

Shankaran

Muro

Bang

Geva

Catenacci

Gupta

. (2015) Correlation of gene expression signatures and clinical outcomes in patients with advanced gastric cancer treated with pembrolizumab (MK-3475). J Clin Oncol 33: 3026.

54.

Shapira-Frommer

Oza

Domchek

Balmana

Patel

Chen

. (2015) A phase II open-label, multicenter study of single-agent rucaparib in the treatment of patients with relapsed ovarian cancer and a deleterious BRCA mutation. J Clin Oncol 33: 5513.

55.

Shen

Pan

Dai

Qin

. (2015) Bevacizumab plus capecitabine and cisplatin in Chinese patients with inoperable locally advanced or metastatic gastric or gastroesophageal junction cancer: randomized, double-blind, phase III study (AVATAR study). Gastric Cancer 18: 168–176.

56.

Smyth

Tan

Cunningham

Wotherspoon

Lin

Okines

. (2013) Magic trial gene expression profiling study. J Clin Oncol 31: 4020.

57.

Smyth

Turner

Peckitt

Pearson

Brown

Chua

. (2015) Phase II multicenter proof of concept study of AZD4547 in FGFR amplified tumours. J Clin Oncol 33: 2508.

58.

Song

Gong

(2002) Relationship between the expression of iNOS,VEGF,tumor angiogenesis and gastric cancer. World J Gastroenterol 8: 591–595.

59.

Tan

Ivanova

Lim

Ong

Deng

Lee

. (2011) Intrinsic subtypes of gastric cancer, based on gene expression pattern, predict survival and respond differently to chemotherapy. Gastroenterology 141: 476–485.

60.

The Cancer Genome Atlas Research Network (2014) Comprehensive molecular characterization of gastric adenocarcinoma. Nature 513: 202–209.

61.

Thuss-Patience

Kretzschmar

Bichev

Deist

Hinke

Breithaupt

. (2011) Survival advantage for irinotecan versus best supportive care as second-line chemotherapy in gastric cancer – a randomised phase III study of the Arbeitsgemeinschaft Internistische Onkologie (AIO). Eur J Cancer 47: 2306–2314.

62.

Van Cutsem

De Haas

Kang

Ohtsu

Tebbutt

Ming Xu

. (2012) Bevacizumab in combination with chemotherapy as first-line therapy in advanced gastric cancer: a biomarker evaluation from the AVAGAST randomized phase III trial. J Clin Oncol 30: 2119–2127.

63.

Van Cutsem

Moiseyenko

Tjulandin

Majlis

Constenla

Boni

. (2006) Phase III study of docetaxel and cisplatin plus fluorouracil compared with cisplatin and fluorouracil as first-line therapy for advanced gastric cancer: a report of the V325 study group. J Clin Oncol 24: 4991–4997.

64.

Waddell

Chau

Cunningham

Gonzalez

Okines

. (2013) Epirubicin, oxaliplatin, and capecitabine with or without panitumumab for patients with previously untreated advanced oesophagogastric cancer (REAL3): a randomised, open-label phase 3 trial. Lancet Oncol 14: 481–489.

65.

Wagner

Unverzagt

Grothe

Kleber

Grothey

Haerting

. (2010) Chemotherapy for advanced gastric cancer. Cochrane Database Syst Rev: CD004064.

66.

Watkins

Irshad

Grigoriadis

Tutt

(2014) Genomic scars as biomarkers of homologous recombination deficiency and drug response in breast and ovarian cancers. Breast Cancer Res 16: 211.

67.

Wilke

Muro

Van Cutsem

Bodoky

Shimada

. (2014) Ramucirumab plus paclitaxel versus placebo plus paclitaxel in patients with previously treated advanced gastric or gastro-oesophageal junction adenocarcinoma (RAINBOW): a double-blind, randomised phase 3 trial. Lancet Oncol 15: 1224–1235.

68.

Wolchok

Kluger

Callahan

Postow

Rizvi

Lesokhin

. (2013) Nivolumab plus ipilimumab in advanced melanoma. N Engl J Med 369: 122–133.

69.

Yao

Kausalya

Sia

Teo

Lee

Ong

. (2015) Recurrent fusion genes in gastric cancer: CLDN18-ARHGAP26 induces loss of epithelial integrity. Cell Rep 12: 272–285.

70.

Ychou

Boige

Pignon

Conroy

Bouché

Lebreton

. (2011) Perioperative chemotherapy compared with surgery alone for resectable gastroesophageal adenocarcinoma: an FNCLCC and FFCD multicenter phase III trial. J Clin Oncol 29: 1715–1721.

71.

Yoon

Bendell

Braiteh

Firdaus

Philip

Cohn

. (2014) Ramucirumab (RAM) plus FOLFOX as front-line therapy (Rx) for advanced gastric or esophageal adenocarcinoma (GE-AC): randomized, double-blind, multicenter phase 2 trial. J Clin Oncol 32: 4004.