MDM2 Amplification Status in a Cohort of Well-Characterized Myxofibrosarcoma: A Clinicopathologic Analysis of 22 Tumors

Abstract

Myxofibrosarcomas (MFS) present as slowly enlarging superficial masses in elderly patients. Even though these tumors fail to exhibit a distinct immunophenotype, diagnosis is straightforward when they present in subcutaneous tissue. Intramuscular MFS, however, are more challenging to diagnose as the differential also includes dedifferentiated liposarcoma with myxoid features. The vast majority of dedifferentiated liposarcomas show MDM2 amplification, whereas limited data exists as to the MDM2 status of MFS. We sought to explore the rate of MDM2 amplification in cases of classic MFS. Our archives were searched for MFS; only subcutaneous well-sampled resections were included. FISH for MDM2 amplification was performed on each tumor. A cohort of myxoid dedifferentiated liposarcoma resections was studied for comparison. Twenty-two MFS arose in patients aged 44 to 85 years. All tumors contained an infiltrative population of atypical cells embedded in a myxoid stroma with curvilinear blood vessels. MDM2 amplification by FISH was identified in 3 (of 22; 14%) tumors. Available follow up on 17 patients (range 1-96 months; median 13 months) revealed 6 patients with local recurrence and 1 with distant metastasis. Of 3 patients with MDM2- amplified MFS, 1 experienced recurrence and died of unrelated causes, while the second was alive without disease 12 months after diagnosis. Even though the rate of MDM2 amplification by FISH in MFS appears to be low, a subset of cases may show this genetic alteration, which pathologists should be aware of to avoid misclassification as myxoid dedifferentiated liposarcomas. Further studies are necessary to determine if amplification status adds prognostic value.

Keywords

myxofibrosarcoma dedifferentiated liposarcoma FISH OncoScan assay

Introduction

Myxofibrosarcomas (MFS) are locally aggressive and potentially metastasizing sarcomas that classically present as slowly enlarging masses in elderly patients and consist of variably atypical spindled cells in an at least focally myxomatous stroma. Most MFS occur in dermal/subcutaneous tissue of the proximal extremities and diagnosis is relatively straightforward in this setting. However, up to one third may arise below the fascia or intramuscularly in the extremity; in this setting the differential diagnoses include dedifferentiated liposarcoma with myxoid features.^1,2 The vast majority of dedifferentiated liposarcomas show MDM2 amplification, whereas limited data exists as to the MDM2 amplification status of MFS.^3–10 Therefore, we sought to explore the rate of MDM2 amplification in cases of classic MFS to determine its utility in this diagnostic setting.

Methods

The Institutional Review Board of the Mayo Clinic approved this study. Institutional and personal consultation (KJF) archives were searched for cases of primary MFS and myxoid dedifferentiated liposarcoma resection specimens without prior treatment. To be included in this study, tumors needed to be well sampled (at least 1 section/cm). Only superficial (above the fascia) MFS cases were included. Cases of dedifferentiated liposarcoma required histologic confirmation of both well-differentiated and dedifferentiated components. Clinical and follow-up information was obtained from medical records and referring institutions.

Interphase Enumeration FISH Method

Each tumor was analyzed for MDM2 copy number using an enumeration strategy. Abbott Molecular CEP 12 (D12Z3) labeled in Spectrum Green and Abbott Molecular MDM2 (12q15) labeled in Spectrum Orange was mixed with LSI/WCP hybridization buffer. Slides were placed in a 90 °C oven for 15 min. Slides were then deparaffinized with xylene (2 times, 15 minutes each) at room temperature (RT), dehydrated in 100% ethanol for 5 minutes at RT, and placed in 10 mM citric acid (pH 6.0) and microwaved for 10 minutes. Following this, the slides were immersed in 2× standard saline citrate (SSC) for 5 minutes at 37 °C followed by digestion in 0.2% pepsin working solution (1.2 g pepsin/600 mL 0.9% NaCl pH 1.5) at 37 °C for 12 minutes. Immediately after digestion, the slides were dehydrated using an ethanol series (70%, 85%, 100%) 2 minutes each at RT. The slide and probe were co-denatured and hybridized overnight. Slides were then washed and DAPI counterstain was applied as well as a glass coverslip. Visualization of the FISH signals was accomplished by use of a fluorescent microscope and images were captured using a FISH imaging system. Two reviewers each analyzed 30 nuclei with FISH signals per sample. For this study, a qualifying nucleus for scoring purposes must contain at least 1 red signal and 1 green signal. Results were determined by calculating the ratio of MDM2 (orange) copy number to CEP 12 (green) signals using an Excel Spreadsheet. A ratio of MDM2 to CEP 12 greater than 1.30 indicated additional copies of were MDM2 present. A ratio greater than 2.0, and the presence of >6 MDM2 signals per cell indicated MDM2 gene amplification. Over 30% of nuclei with 3 or more green signals were indicative of aneusomy 12. A ratio of less 0.80 demonstrated loss of MDM2 relative to CEP 12. Ratios between 0.80 and 1.30 were considered normal.

OncoScan Assay Method

The OncoScan® FFPE Assay Kit (Affymetrix; Santa Clara, CA) was applied to isolated DNA. The technicalities of the molecular inversion probe (MIP) assay have been previous described.¹¹ Briefly, a MIP targeting a unique SNP or base pair of interest anneals to isolated DNA and circularizes with its complementary nucleotide. Single stranded material is destroyed, and the circular probe is then released, cleaved, becomes inverted, and is amplified using universal primers. The biotinylated oligo is hybridized overnight to a microarray. Two microarray chips are used per sample and the entire process takes two-and-a-half days to complete. The genome-wide functional resolution of this array is approximately 500 kilobases for non-mosaic deletions and non-mosaic duplications. However, functional resolution of this array varies significantly dependent upon size of the abnormality, probe density in region, percentage of abnormal cells, and quality of the DNA obtained. Mosaic clonal abnormalities, especially those that are represented in a minor fraction of the sample, may not be detected. Deletions larger than 1 megabase, duplications larger than 2 megabases, and copy neutral loss of heterozygosity (cnLOH) larger than 10 megabases are generally reported. However, complex genomic alterations may be reported in aggregate, and well documented pathogenic constitutional and/or acquired abnormalities of any size may also be reported. All data were analyzed and reported using the February 2009 NCBI human genome build 37.1 (hg19). The genome coordinates described are best estimates and may not represent precise breakpoints, especially for abnormalities detected in a low percentage of cells.

Results

Myxofibrosarcoma

Overall, 22 resection specimens of MFS were evaluated and the clinicopathologic features of these tumors are summarized in Table 1. All tumors showed classic morphology of MFS including an infiltrative and multinodular growth pattern within subcutaneous fat, composed of variably atypical spindle cells admixed with curvilinear blood vessels (Figures 1 to 3). At least 1 low power field containing myxoid stroma was appreciated in each tumor. The patients’ age range was 44 to 85 years with a median of 70.5 years. The tumors occurred almost equally in men (n = 12) and women (n = 10). Tumor size ranged from 1.1 to 13.8 cm (median of 3.8 cm). Thirteen MFS occurred in the lower extremity (59%), 7 occurred in the upper extremity (32%), and 2 were located in the trunk (9%). Seventeen of 22 tumors were primary and 5 represented a local recurrence. The mitotic rate (per 10 high power fields) ranged between 0 and 73 (median of 12). The percentage of tumor necrosis per tumor was as follows: 0%, n = 11; 1% to 50%, n = 9; >50%, n = 2. Seven of 22 tumors were FNCLCC grade 1, 4 were FNCLCC grade 2, and 11 were FNCLCC grade 3. Of 17 patients with available follow-up information (1-96 months; median 13 months), 11 were alive with no evidence of disease and 6 patients experienced at least 1 recurrence. One patient developed distant pulmonary metastases. Three patients were deceased at the end of follow up, including the patient with distant metastases, who died of disease. FISH studies for MDM2 showed amplification in 3 of 22 tumors (MFS10, MFS18 and MFS 22 in Table 1; Figures 1 to 4). In MFS10, the MDM2/CEP 12 ratio was 3.19 (average number of MDM2 signals 17.5), in MFS18, the MDM2/CEP 12 ratio was 2.14 (average number of MDM2 signals 16.1), and in MFS22 the MDM2/CEP 12 ratio was 12.7 (average number of MDM2 signals 21.0). Imaging and gross examination did not identify a fatty component in these 3 MFS with MDM2 amplification by FISH. Tumors MFS18 and MFS22 represented primary lesions, while MFS10 was a recurrence.

Figure 1.

Images from a classic myxofibrosarcoma (MFS10) located in subcutaneous soft tissue of the right forearm (A) which showed MDM2 amplification by FISH and OncoScan. The tumor showed a multinodular growth pattern with infiltrative tumor tentacles (B), curvilinear blood vessels (C), and atypical spindle cells with admixed pseudolipoblasts (D).

Figure 2.

Histologic sections from a lower back myxofibrosarcoma (MFS18) showed a multinodular growth pattern with alternating hyper and hypocellular areas (A). Higher magnification illustrates hyperchromatic spindled cells with marked atypia (B). This tumor showed MDM2 amplification by FISH but not by OncoScan.

Figure 3.

MFS22, which showed MDM2 amplification by FISH and OncoScan, arose in the superficial thigh and showed a necrotic high grade malignancy with surface ulceration (A). Medium power images demonstrate admixed myxoid and solid components (B). Closer inspection demonstrates plump malignant cells with occasional prominent nucleoli (C).

Figure 4.

FISH (CEN 12(green)/MDM2(orange)[12q15]) from a myxofibrosarcoma with MDM2 amplification (MFS 10). Image indicates nuclei with 10–21 + orange and 2–8 green signal. Inset provides a closer look at signal amplification.

Table 1.

Myxofibrosarcoma Tumors, Clinicopathological Features: MFS 10, 18 and 22 Showed MDM2 Gene Amplification by FISH. MSF18 Did Not Show MDM2 Amplification by OncoScan Assay.

Patients	Age (years)	Sex	Site	Size (cm)	Depth	MDM2 FISH Amplification	MDM2/CEP12 Ratio	Epithelioid Morphology	FNCLCC Grade	Outcome Recurrence/Status/Follow Up by Months
MFS 1	60	M	L calf	3.8	Superficial	No	1.01	No	1	No/ANED/13
MFS2	64	F	R forearm	3	Superficial	No	1.02	No	1	Yes/AWD/24
MFS3	71	M	L forearm	1.1	Superficial	No	1.38	No	3	Yes/ANED/36
MFS4	84	M	L forearm	3.6	Superficial	No	1.0	No	1	No/ANED/29
MFS5	70	F	R thigh	3.6	Superficial	No	1.09	No	2	Yes/ ANED/96
MFS6	59	F	L thigh	3.5	Superficial	No	1.07	No	3	No/ ANED/48
MFS7	64	M	L hip	3.1	Superficial	No	0.57	No	3	No/ANED/8
MFS8	84	F	R leg	11	Superficial	No	1.41	Yes	3	Yes/Met and DOD/7
MFS9	81	M	R forearm	6.8	Superficial	No	1.55	No	1	Yes/Cause of death unclear/72
MFS10	85	F	R forearm	1.7	Superficial	Yes	3.19	No	1	Yes/DOO/ 84
MFS11	77	F	L calf	3.2	Superficial	No	0.99	No	2	No/ANED/3
MFS12	47	M	R inguinal	6.2	Superficial	No	1.06	No	1	No/ANED/1
MFS13	66	F	R thigh	3.8	Superficial	No	1.04	No	1	No/ANED/8
MFS14	75	M	L leg	2.5	Superficial	Not	1.55	No	3	No/ANED/1
MFS15	44	F	R hip	4	Superficial	No	1.67	No	3	No/ANED/3
MFS16	79	F	L thigh	11	Superficial	No	1.6	No	3	No/ANED/24
MFS17	74	F	R knee	4.3	Superficial	No	1.44	No	2	Not available
*MFS18	64	M	Lower back	5.5	Superficial	Yes	*2.14	No	3	No/ANED/12
MFS19	72	M	L upper back	7	Superficial	No	1.27	Yes	3	Not available
MFS20	49	M	L upper arm	3.2	Superficial	No	0.99	No	2	Not available
MFS21	77	M	L forearm	8	Superficial	No	1.09	Yes	3	Not available
MFS22	67	M	L thigh	13.8	Superficial	Yes	12.7	No	3	Not available

Abbreviations: M, male; F, female; R, right; L, left; ANED, alive no evidence of disease; AWD, alive with disease, DOD, died of disease; DOO, died of other causes; Met, metastasis; * MSF18 did not show MDM2 amplification by OncoScan assay.

OncoScan assay confirmed MDM2 amplification in MFS10 and MFS22, while MFS18 was negative for MDM2 amplification. Interestingly careful re-review of FISH images for MSF18 showed increased CEP12 signal as well, potentially indicating gains of chromosome 12 or co-amplification of the centromere probe in contrast to pure MDM2 amplification. Since OncoScan assay in MFS18 did not detect MDM2 amplification or 15 or greater copies of chromosome 12, the discordant results are best explained by heterogeneity in tumor nuclei scored by FISH and/or a low level subclone not detectable by chromosomal microarray. All 3 tumors additionally showed complex molecular karyotypes with subclonal gains and losses, including loss of RB1 (3/3) and CDKN2A and CDKN2B (2/3).

Dedifferentiated Liposarcoma

Eleven dedifferentiated liposarcoma with myxoid features (7 males, 4 females; age range: 36-85 years, median 71 years) were identified and investigated for comparison. The tumors were located in the retroperitoneum (n = 6), abdominal cavity (n = 4), and intramuscularly in the extremity (n = 1). Histologic review revealed biphasic tumors showing areas of well-differentiated liposarcoma juxtaposed to non-lipogenic foci composed of malignant spindle cells in a myxoid background (Figure 5). MDM2 amplification was identified by FISH in all specimens (11/11). In differentiated liposarcoma tumors with myxoid features (entire cohort, n = 11), the MDM2/CEP 12 ratio was between 5.7 and 12.9, while average number of MDM2 signals per cell ranged from 13 to 21.

Figure 5.

Example of a myxoid dedifferentiated liposarcoma which shows a biphasic appearance composed of mature adipose tissue with atypical hyperchromatic stromal cells (A) admixed with a high grade myxoid sarcoma (B). High power examination shows areas indistinguishable from myxofibrosarcoma with atypical hyperchromatic spindle cells in a myxomatous background with a prominent curvilinear vasculature (C).

Discussion

Pleomorphic sarcomas, including MFS, generally show complex molecular signatures.^12–14 Alterations in genes in the p53 signaling, cell cycle regulators, and RTK-PI3K pathway appear to be shared among these sarcomas. By integrated genetic and epigenetic analysis, MFS show frequent alterations in p53 signaling and cell cycle check points including RB1 and CDKN2A/B.^15–17 Dedifferentiated liposarcomas, on the other hand, consistently show MDM2 amplification.^6,7,18,19 This finding is not entirely specific, though, and has also been described in other sarcomas including malignant peripheral nerve sheath tumor,²⁰ leiomyosarcoma,²¹ intimal sarcoma,^22,23 low grade central osteosarcoma,^24,25 parosteal osteosarcoma²⁶ and endometrial stromal sarcoma.^27,28 A handful of studies in the literature have shown that a small subset of MFS has MDM2 amplification, including, a comprehensive genetic report by Ogura et al which found 7 of 116 MFS to have this feature.¹⁵ However, detail as to the degree of histologic sampling and/or depth of the lesions is lacking, leaving open the possibility that MDM2-amplified cases may actually represent the myxoid variant of dedifferentiated liposarcoma.^8–10,15,29 In fact, in the study by Song et al, 1 MDM2-amplified retroperitoneal sarcoma initially classified as MFS was reclassified as dedifferentiated liposarcoma.¹⁰ We aimed to further clarify the rate of MDM2 amplification in a series of well-characterized superficial MFS. To this end, we confirm that a minority of MFS do in fact show MDM2 amplification.

While numerous myxoid sarcomas have a distinct immunoprofile or characteristic genetic findings, MFS is still a diagnosis based on histologic examination. One of its closest morphologic mimics is myxoid dedifferentiated liposarcoma. Dedifferentiated liposarcoma rarely occurs above the fascia, and MFS is virtually nonexistent in deep central sites, so differentiating these entities becomes most critical at intramuscular sites in the extremities. We show that the presence of MDM2 amplification favors myxoid dedifferentiated liposarcoma over MFS; however, diligent sampling and careful search for a well-differentiated liposarcoma is also suggested as this feature is the only definitive way to differentiate these two entities. Additionally, on biopsy material, correlation with imaging regarding the presence of a lipomatous component may be helpful. If such clinical data is not available, one should be cautious about rendering a diagnosis of dedifferentiated liposarcoma, especially in a superficial location, based on the presence of MDM2 amplification. On the other hand, in deep-seated central sites (eg, retroperitoneum) where dedifferentiated liposarcomas far outnumber other sarcomas, MDM2 data is much more informative.

MDM2-amplified MFS in our cohort failed to show any clinical differences from their non-amplified counterparts. They occurred over a broad age range and arose in both the trunk and extremities. Furthermore, the behavior of this subset was variable. One patient experienced recurrence while another remained free of disease at 12 months; the third patient lacked follow-up.

In our study, we used OncoScan data to confirm the presence of MDM2 amplification. Interestingly, 2 of the 3 tumors showed concordant results, while MDM2 amplification was absent in the third one (MSF18). Re-review of FISH images for the discordant tumor showed additional MDM2 signal (>20) in the context of additional copy gain of centromere 12 (15-20). This finding indicated likely co-amplification of MDM2/CEP 12 with a ratio less than 2 (cut off >2.0), however; OncoScan assay did not detect MDM2 amplification or 15 or greater copies of chromosome 12 in the discordant tumor (MSF18). Signal heterogeneity with a subpopulation of tumor cells showing increased MDM2 signal on FISH may lead to false positive results. The subsequent increase in MDM2 signal and borderline MDM2/CEP 12 ratio should be interpreted with caution, triggering a confirmatory method such as OncoScan.

Genomic alterations including MDM2 amplification introduce new targets for potential treatment options.^30,31 MDM2/CDK4 inhibitors such as nutlin,³² siremadlin,³³ and ribociclib³⁴ offer therapeutic efficacy for well-differentiated and dedifferentiated liposarcomas. Given the similar underlying genetic alteration in MFS with MDM2 amplifications, such novel agents may potentially be beneficial for these patients as well.

Conclusion

We sought to evaluate the rate of MDM2 amplification in a group of well-characterized myxofibrosarcomas. While the rate of MDM2 amplification in our cohort was low, these tumors may rarely show this genetic alteration. Additional studies are necessary to determine if the presence of MDM2 amplification in myxofibrosarcoma has prognostic value.

Footnotes

Acknowledgment

The Authors are grateful to Mayo Cytogenetics Core Laboratory.

Author's Note

Nooshin K. Dashti is currently affiliated to the Department of Pathology and Laboratory Medicine, Dartmouth-Hitchcock Medical Center, Lebanon, NH and Geisel School of Medicine at Dartmouth College, Hanover, NH, USA.

Declaration of Conflicting Interests

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

Ethical Approval

This study was performed in accordance with current ethical guidelines of the Declaration of Helsinki and the requirements of the Institutional Review Board of Mayo Clinic, Rochester, MD, USA (Approval number IRB18-006968).

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Nooshin K. Dashti MD

Ahmed Bakhshwin

Patricia Greipp

Karen J. Fritchie

References

Mentzel

Calonje

Wadden

, et al. Myxofibrosarcoma. Clinicopathologic analysis of 75 cases with emphasis on the low-grade variant. Am J Surg Pathol. 1996;20(4):391-405.

Angervall

Kindblom

Merck

Myxofibrosarcoma. A study of 30 cases. Acta Pathol Microbiol Scand A. 1977;85A(2):127-140.

McCormick

Mentzel

Beham

Fletcher

. Dedifferentiated liposarcoma. Clinicopathologic analysis of 32 cases suggesting a better prognostic subgroup among pleomorphic sarcomas. Am J Surg Pathol. 1994;18(12):1213-1223.

Meis-Kindblom

Sjögren

Kindblom

L-G

, et al. Cytogenetic and molecular genetic analyses of liposarcoma and its soft tissue simulators: recognition of new variants and differential diagnosis. Virchows Arch. 2001;439(2):141-151.

Shimada

Ishizawa

Matsumura

Hasegawa

Hirose

. The value of MDM2 and CDK4 amplification levels using real-time polymerase chain reaction for the differential diagnosis of liposarcomas and their histologic mimickers. Hum Pathol. 2006;37(9):1123-1129.

Sirvent

Coindre

J-M

Maire

, et al. Detection of MDM2-CDK4 amplification by fluorescence in situ hybridization in 200 paraffin-embedded tumor samples: utility in diagnosing adipocytic lesions and comparison with immunohistochemistry and real-time PCR. Am J Surg Pathol. 2007;31(10):1476-1489.

Weaver

Downs-Kelly

Goldblum

, et al. Fluorescence in situ hybridization for MDM2 gene amplification as a diagnostic tool in lipomatous neoplasms. Mod Pathol. 2008;21(8):943-949.

Oda

Takahira

Kawaguchi

, et al. Altered expression of cell cycle regulators in myxofibrosarcoma, with special emphasis on their prognostic implications. Hum Pathol. 2003;34(10):1035-1042.

Kimura

Dobashi

Nojima

, et al. Utility of fluorescence in situ hybridization to detect MDM2 amplification in liposarcomas and their morphological mimics. Int J Clin Exp Pathol. 2013;6(7):1306-1316.

10.

Song

Cho

K-J

Lee

J-S

Song

. Application of MDM2 fluorescence in situ hybridization and immunohistochemistry in distinguishing dedifferentiated liposarcoma from other high-grade sarcomas. Appl Immunohistochem Mol Morphol. 2017;25(10):712-719.

11.

Wang

Sapolsky

Venkatapathy

Siddiqui

Shen

Jiang

. OncoScan™ FFPE express 2.0: a cancer-focused whole-genome copy number platform requiring only 75 ng of input DNA from FFPE samples. Cancer Res. 2012;72(8_Suppl.):1259-1259.

12.

Helman

Meltzer

. Mechanisms of sarcoma development. Nat Rev Cancer. 2003;3(9):685-694.

13.

Gibault

Pérot

Chibon

, et al. New insights in sarcoma oncogenesis: a comprehensive analysis of a large series of 160 soft tissue sarcomas with complex genomics. J Pathol. 2011;223(1):64-71.

14.

Taylor

Barretina

Maki

Antonescu

Singer

Ladanyi

. Advances in sarcoma genomics and new therapeutic targets. Nat Rev Cancer. 2011;11(8):541-557.

15.

Ogura

Hosoda

Arai

, et al. Integrated genetic and epigenetic analysis of myxofibrosarcoma. Nat Commun. 2018;9(1):1-11.

16.

Heitzer

Sunitsch

Gilg

, et al. Expanded molecular profiling of myxofibrosarcoma reveals potentially actionable targets. Mod Pathol. 2017;30(12):1698-1709.

17.

Okada

Kim

Y-M

, et al. Rb and p53-deficient myxofibrosarcoma and undifferentiated pleomorphic sarcoma require Skp2 for survival. Cancer Res. 2020;80(12):2461-2471.

18.

Pedeutour

Forus

Coindre

, et al. Structure of the supernumerary ring and giant rod chromosomes in adipose tissue tumors. Genes Chromosomes Cancer. 1999;24(1):30-41.

19.

Binh

MBN

Sastre-Garau

Guillou

, et al. MDM2 and CDK4 immunostainings are useful adjuncts in diagnosing well-differentiated and dedifferentiated liposarcoma subtypes: a comparative analysis of 559 soft tissue neoplasms with genetic data. Am J Surg Pathol. 2005;29(10):1340-1347.

20.

Wallander

Tripp

Layfield

. MDM2 amplification in malignant peripheral nerve sheath tumors correlates with p53 protein expression. Arch Pathol Lab Med. 2012;136(1):95-99.

21.

Ragazzini

Gamberi

Pazzaglia

, et al. Amplification of CDK4, MDM2, SAS and GLI genes in leiomyosarcoma, alveolar and embryonal rhabdomyosarcoma. Histol Histopathol. 2004;19(2):401-411.

22.

Bode-Lesniewska

Zhao

Speel

, et al. Gains of 12q13–14 and overexpression of mdm2 are frequent findings in intimal sarcomas of the pulmonary artery. Virchows Arch. 2001;438(1):57-65.

23.

Neuville

Collin

Bruneval

, et al. Intimal sarcoma is the most frequent primary cardiac sarcoma: clinicopathologic and molecular retrospective analysis of 100 primary cardiac sarcomas. Am J Surg Pathol. 2014;38(4):461-469.

24.

Dujardin

Binh

MBN

Bouvier

, et al. MDM2 and CDK4 immunohistochemistry is a valuable tool in the differential diagnosis of low-grade osteosarcomas and other primary fibro-osseous lesions of the bone. Mod Pathol. 2011;24(5):624-637.

25.

Park

H-R

Jung

Bertoni

, et al. Molecular analysis of p53, MDM2 and H-ras genes in low-grade central osteosarcoma. Pathol Res Pract. 2004;200(6):439-445.

26.

Wunder

Eppert

Burrow

Gogkoz

Bell

Andrulis

. Co-amplification and overexpression of CDK4, SAS and MDM2 occurs frequently in human parosteal osteosarcomas. Oncogene. 1999;18(3):783-788.

27.

Schoolmeester

Sciallis

Greipp

, et al. Analysis of MDM2 amplification in 43 endometrial stromal tumors: a potential diagnostic pitfall. Int J Gynecol Pathol. 2015;34(6):576-583.

28.

Kommoss

Chang

Stichel

, et al. Endometrial stromal sarcomas with BCOR-rearrangement harbor MDM2 amplifications. J Pathol Clin Res. 2020;6(3):178-184.

29.

Sioletic

Dal Cin

Fletcher

Hornick

. Well-differentiated and dedifferentiated liposarcomas with prominent myxoid stroma: analysis of 56 cases. Histopathology. 2013;62(2):287-293.

30.

Ray-Coquard

Blay

J-Y

Italiano

, et al. Effect of the MDM2 antagonist RG7112 on the P53 pathway in patients with MDM2-amplified, well-differentiated or dedifferentiated liposarcoma: an exploratory proof-of-mechanism study. Lancet Oncol. 2012;13(11):1133-1140.

31.

Barretina

Taylor

Banerji

, et al. Subtype-specific genomic alterations define new targets for soft-tissue sarcoma therapy. Nat Genet. 2010;42(8):715-721.

32.

Müller

Paulsen

Noordhuis

Pedeutour

Sæter

Myklebost

. Potential for treatment of liposarcomas with the MDM2 antagonist nutlin-3A. Int J Cancer. 2007;121(1):199-205.

33.

Abdul Razak

Bauer

Suarez

, et al. Co-targeting of MDM2 and CDK4/6 with siremadlin and ribociclib for the treatment of patients with well-differentiated or dedifferentiated liposarcoma: results from a proof-of-concept, phase Ib study. Clin Cancer Res. 2022;28(6):1087-1097.

34.

Assi

Kattan

Rassy

, et al. Targeting CDK4 (cyclin-dependent kinase) amplification in liposarcoma: a comprehensive review. Crit Rev Oncol Hematol. 2020;153:103029.