Cytopathological Features of SMARCA4 -Deficient Thoracic Sarcoma: Report of 2 Cases and Review of the Literature

Abstract

SMARCA4-deficient thoracic sarcoma (SMARCA4-DTS) is a recently described entity of thoracic sarcomas with an undifferentiated rhabdoid morphology and SMARCA4 inactivation. Regardless of some reports about the histopathological findings so far, there have been only a few reports about the cytological features. In this article, we present the pathological features of 2 SMARCA4-DTS cases, including the cytological findings. Histopathologically, the tumor cells showed atypical loosely cohesive large epithelioid cells focally with geographic necrosis. Some cells were characterized by rhabdoid cells. Both patients showed intrathoracic masses with a history of smoking, and loss of SMARCA4 expression was confirmed with histopathological specimens. Immunohistochemically, tumor cells of both cases were at least focally positive for cytokeratin, CD34, CD99, synaptophysin, SOX2, and SALL4. In addition, tumor cells demonstrated significantly reduced expression of BRG1/SMARCA4 and SMARCA2. In conclusion, SMARCA4-DTS should be taken into consideration in the differential diagnosis of tumors with undifferentiated rhabdoid morphology involving the thoracic region.

Keywords

SMARCA4-deficient thoracic sarcoma SWI/SNF complex rhabdoid cells imprint cytology immunohistochemistry

Introduction

SMARCA4-deficient thoracic sarcoma (SMARCA4-DTS) is a recently proposed entity of soft tissue sarcomas characterized by inactivation of SMARCA4, a gene encoding an ATPase subunit of the switch/sucrose non-fermenting (SWI/SNF) chromatin remodeling complexes.¹ The cytomorphologic characteristics of SMARCA4-DTS have been reported to be undifferentiated and sometimes rhabdoid. There have been still only a few reports about the histological features of SMARCA4-DTS so far.^2-6

We report 2 rare SMARCA4-DTS cases of this new entity, including the cytological findings.

Case Reports

Case 1

Clinical History

A 50-year-old man without any history of malignancies was seen with complaints of anorexia, hoarseness, and left-sided back pain commencing 2 months prior to hospital admission. He had a history of smoking 20 cigarettes per day for 38 years. Computed tomography scan revealed an intrathoracic comprehensive mass occupying the left lung apex and the anterior mediastinum (Figure 1A). Definitive diagnosis was not obtained by the biopsy of the enlarged metastatic cervical lymph node. Chemoradiotherapy was performed, but without tumor reduction. He died because of the respiratory failure a month after the chemotherapy was started. An autopsy was performed.

Cytologic Findings of Biopsy Specimen (Touch Imprint Cytology)

The smears were hypercellular and showed many atypical round-to-ovoid cells having prominent nucleoli singly or in loosely cohesive clusters with a necrotic background (Figure 1E and F). The atypical cells harbored cytoplasm slightly dense-stained with light green, and nucleoli showing vesicular chromatin. The tumor cells were relatively monotonous focally with pleomorphism. Some atypical cells demonstrated eccentric nuclei suggestive of a rhabdoid appearance.

Histopathologic Findings

Biopsy of the left cervical lymph node showed atypical loosely cohesive large epithelioid cells focally with geographic necrosis (Figure 1C). Atypical cells exhibited lightly eosinophilic cytoplasm and prominent nucleoli. The autopsy finding showed a white solid 10 × 7 × 6.5 cm mass occupying mainly the left anterior mediastinum, pleura, and lung (Figure 1B). Histologically, in addition to the findings of the lymph node biopsy mentioned above, rhabdoid tumor cells were also found (Figure 1D). Metastasis to the pancreas, bilateral adrenals, omentum, mesentery, digestive tract, and paraaortic lymph nodes was detected. The results of the immunostaining for tumor cells are shown in Table 1. Immunohistochemically, tumor cells were focally positive for cytokeratin (AE1/AE3 and CAM5.2), and diffusely positive for CD34, CD99, synaptophysin, SOX2, and SALL4 (Figure 2A-D). In addition, tumor cells demonstrated significantly reduced expression of BRG1/SMARCA4 and SMARCA2 (Figure 2E and F).

Table 1.

Immunohistochemical Results for Case 1 and Case 2.

Antibody	Case 1	Case 2
CAM5.2	+, focal (biopsy: <5%, autopsy: 20%)	+, focal (15%)
AE1/AE3	+, focal (biopsy: <5%, autopsy: 20%)	+, focal (20%)
Claudin4	−	−
SALL4	+	+
SOX2	+	+
Synaptophysin	+	+
Chromogranin A	−	−
Insulinoma-associated protein 1 (INSM1)	−	−
CD99	+	+
CD34	+	+, focal (30%)
SMARCA4 (BRG1) deficiency	+	+
SMARCA2 deficiency	+	+

A cytogenetic study with G-banding revealed that all of the 20 tumor cells had complex karyotypes. The representative abnormality karyotype was as follows: 64,XY,-X,-2, add(3)(p25), +del(3)(p11),-4, add(5)(q11.2)x2,-6, add(6)(p23), add(7)(q22),-8,-9, inv(9)(p12q13),-10, add(10)(q24), add(11)(q23), add(12)(p11.2), +add(12)(q13), add(12)(q24.1)x2,-13,-14, add(15)(p11.2), add(15)(q22),-16,-17,+18,-19,-20,-21, add(22)(p11.2),+11mar.

Case 2

Clinical History

A 70-year-old man without any history of malignancies felt the left chest pain commencing 1 month previous to hospital admission. He had a history of smoking 20 cigarettes per day for 54 years. Computed tomography scan revealed intrathoracic compressive masses at the left chest wall. He received chemotherapy after biopsy of the left pleura, but without tumor reduction. He died 11 months later. An autopsy was not performed.

Cytologic Findings (Touch Imprint Cytology)

The smears showed a morphology similar to case 1 (Figure 3A).

Histopathologic Findings

Biopsy of the tumor at the left pleura showed sheets of atypical round cells with a few cells showing rhabdoid morphology (Figure 3). Geographic necrosis was focally found. The results of the immunostaining for tumor cells are shown in Table 1.

Discussion

SMARCA4-DTS is a distinct entity of undifferentiated thoracic malignancies initially proposed by Le Loarer et al in 2015.¹ SMARCA4-DTSs show SMARCA4 inactivation presenting as compressive tumors often involving the mediastinum, with or without lung involvement, occurring in young patients and displaying aggressive behavior. The SMARCA4 gene encodes the BRG1 protein, which is 1 of the 2 mutually exclusive catalytic subunits of the SWI/SNF chromatin-remodeling complex. The other catalytic subunit is BRM, encoded by the SMARCA2 gene. Inactivation of SMARCA4 has been reported in several aggressive tumors with high-grade undifferentiated morphology, including small cell carcinoma of the ovary, hypercalcemic type (SCCOHT), and a subset of atypical teratoid-rhabdoid tumors of the central nervous system. The SMARCA4 gene is located on chromosome 19p13, and the SMARCA2 gene is located on chromosome 9p24. In case 1, abnormalities, such as monosomy, were confirmed in chromosomes 9 and the 19 by G-banding. SMARCA4 mutation and/or loss of SMARCA4 immunoreactivity were reported to be found in 10% of lung carcinomas, correlated with poor prognosis.^7-10 Le Loarer et al found that SMARCA4-DTSs were genetically distinct from lung carcinomas and displayed a closer molecular relationship to SCCOHT and malignant rhabdoid tumor.¹ According to previous reports, SMARCA4-DTS often affects young adults with a history of heavy smoking, pulmonary emphysema/bullae, and histopathologically present as geographical necrosis and rhabdoid cells.^1-6 Discrimination between SMARCA4-DTS and SMARCA4-deficient lung carcinoma from the previous studies is presented in Table 2.² Unlike SMARCA4-DTS, most SMARCA4-deficient lung carcinomas showed cohesive solid sheets of epithelial cells with enhanced pleomorphism. The differential immunoprofile included staining of cytokeratin (diffuse vs focal), TTF-1, CD34, SALL4, SOX2, SMARCA2, and claudin-4. In contrast to lung carcinomas with SMARCA4 inactivation, SMARCA4-DTS cases were reported to show SMARCA2 co-deficiency. To reflect it, SMARCA2 expression was found to be deficient for immunostaining in almost all SMARCA4-DTS cases. Our 2 cases expressed CD34, SOX2, and SALL4, while they lacked SMARCA2 and claudin-4 expression. Clinical and histological features of our cases were highly similar to those described in the previous studies in terms of the location, smoking history, imaging findings, undifferentiated/rhabdoid histology, and poor prognosis.^1-6 Thus, considering clinical and pathological findings, they were diagnosed with SMARCA4-DTS.

Table 2.

Clinical and Immunohistochemical Features of SMARCA4-Deficient Thoracic Sarcoma and SMARCA4-Deficient Lung Carcinoma Among Studied Entities,² and Results of Immunohistochemistry for Case 1 and Case 2.

	SMARCA4-Deficient Thoracic Sarcoma	SMARCA4-Deficient Lung Carcinoma	Case 1	Case 2
Sex	Male-dominated (11:1)	Male-dominated (11:1)	Male	Female
Median age in years (range)	39 (27-82)	55.5 (44-69)	58	74
Primary site	Thorax or abdominal cavity	Lung	Thorax (mediastinum, lung, and pleura)	Mediastinum, pleura
SMARCA4 deficiency	+ (100%)	+ (100%)	+	+
SMARCA2 deficiency	+ (92%)	+ (8%)	+	+
Others	CD34(+) (80%)SOX2(+) (80%)SALL4(+) (80%)p53(+) (70%)TTF-1(+) (10%)Claudin4(−)	CD34(−)SOX2(+) (33%)SALL4(−)TTF-1(+) (50%)Claudin4(+) (100%)CK7(+), HepPar-1(+)	CD34(+)/SALL4(+)/SOX2(+)/p53(−)/TTF-1(−)/Claudin4(−)/CK7(−)/HepPar-1(−)/Synaptophysin(+)/CD99(+)	CD34(+, focal)/SALL4(+)/SOX2(+)/p53(+)/TTF-1(−)/Claudin4(−)/CK7(−)/HepPar-1(−)/Synaptophysin(+)/CD99(+)

There have been only a few reports about the cytological features of SMARCA4-DTS. Recently, Matsushita and Kuwamoto reported that the cytology of SMARCA4-DTS was characterized by atypical round or polygonal cells that appear singly or in loose clusters, enlarged nuclei with vesicular nuclei, prominent nucleoli, and some cells demonstrating rhabdoid morphology.⁵ The findings of our cases resembled these features in a necrotic background.

To date, there has been a clinical trial available for patients with SMARC-deficient tumors with an inhibitor to the histone-lysine N-methyltransferase Enhancer of Zeste Homolog 2 or EZH2, and alternative targeted therapies are under development for tumors deficient of SMARCA4 expression.^11-14 SMARCA4-DTSs behave aggressively and have a prognosis worse than other poorly differentiated thoracic tumors. The identification of SMARCA4-DTS is important prognostically and therapeutically.

In summary, we report a rare case of SMARCA4-DTS. This newly described entity needs to be taken into consideration in the differential diagnosis of tumors with undifferentiated rhabdoid morphology involving the thoracic region. Careful clinicopathological assessment including an immunohistochemical panel (eg, SMARCA4, SMARCA2, cytokeratin, CD34, SALL4, SOX2, and Claudin 4) would assist accurate diagnosis of SMARCA4-DTS even in small biopsies. In our 2 cases, tumor cells were immunopositive for synaptophysin and CD99. Yoshida et al and Perret et al reported that there were some cases that were immunopositive for synaptophysin and CD99.^2,6 In diagnosing such cases, other malignant small round cell tumors including Ewing’s sarcoma and small cell carcinoma will need to be ruled out. Accumulation and the analysis of SMARCA4-DTS cases will be expected in future for prognostic prediction and development of specific therapies.

Footnotes

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.

Funding

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

Ethical Approval

Not applicable, because this article is a case report.

Informed Consent

Written informed consent was obtained from the patient for publication of this case report and accompanying images.

Trial Registration

Not applicable, because this article does not contain any clinical trials.

ORCID iD

Maiko Takeda

References

Le Loarer

Watson

Pierron

et al. SMARCA4 inactivation defines a group of undifferentiated thoracic malignancies transcriptionally related to BAF-deficient sarcomas. Nat Genet. 2015;47:1200-1205.

Yoshida

Kobayashi

Kubo

et al. Clinicopathological and molecular characterization of SMARCA4-deficient thoracic sarcomas with comparison to potentially related entities. Mod Pathol. 2017;30:797-809.

Kuwamoto

Matsushita

Takeda

et al. SMARCA4-deficient thoracic sarcoma: report of a case and insights into how to reach the diagnosis using limited samples and resources. Hum Pathol. 2017;70:92-97.

Sauter

Graham

Larsen

Jenkins

Roden

Boland

JM.

SMARCA4-deficient thoracic sarcoma: a distinctive clinicopathological entity with undifferentiated rhabdoid morphology and aggressive behavior. Mod Pathol. 2017;30:1422-1432.

Matsushita

Kuwamoto

. Cytologic features of SMARCA4-deficient thoracic sarcoma: a case report and comparison with other SWI/SNF complex-deficient tumors. Acta Cytol. 2018;62:456-462.

Perret

Chalabreysse

Watson

et al. SMARCA4-deficient thoracic sarcomas: clinicopathologic study of 30 cases with an emphasis on their nosology and differential diagnoses. Am J Surg Pathol. 2019;43:455-465.

Fukuoka

Fujii

Shih

et al. Chromatin remodeling factors and BRM/BRG1 expression as prognostic indicators in non-small cell lung cancer. Clin Cancer Res. 2004;10:4314-4324.

Medina

Carretero

Fraga

Esteller

Sidransky

Sanchez-Cespedes

. Genetic and epigenetic screening for gene alterations of the chromatin-remodeling factor, SMARCA4/BRG1, in lung tumors. Genes Chromosomes Cancer. 2004;41:170-177.

Medina

Romero

Kohno

et al. Frequent BRG1/SMARCA4-inactivating mutations in human lung cancer cell lines. Hum Mutat. 2008;29:617-622.

10.

Reisman

Sciarrotta

Wang

Funkhouser

Weissman

. Loss of BRG1/BRM in human lung cancer cell lines and primary lung cancers: correlation with poor prognosis. Cancer Res. 2003;63:560-566.

11.

Agulnic

Tannir

Pressey

et al. A phase II, multicenter study of the EZH2 inhibitor tazemetostat in adult subjects with INI1-negative tumors or relapsed/refractory synovial sarcoma. J Clin Oncol. 2016;34(15 suppl):TPS11071. doi:10.1200/JCO.2016.34.15_suppl.TPS11071

12.

Yamamichi

Yamamichi-Nishina

Mizutani

et al. The Brm gene suppressed at the post-transcriptional level in various human cell lines is inducible by transient HDAC inhibitor treatment, which exhibits antioncogenic potential. Oncogene. 2005;24:5471-5481.

13.

Gramling

Rogers

Liu

Reisman

. Pharmacologic reversal of epigenetic silencing of the anticancer protein BRM: a novel targeted treatment strategy. Oncogene. 2011;30:3289-3294.

14.

Gramling

Reisman

. Discovery of BRM targeted therapies: novel reactivation of an anti-cancer gene. Lett Drug Des Discov. 2011;8:93-99.