Usefulness of cell block examination for the cytological diagnosis of thoracic SMARCA4‐deficient undifferentiated tumor: A case report

Abstract

SMARCA4‐deficient undifferentiated tumor (SMARCA4‐UT) is a high‐grade malignant neoplasm showing undifferentiated or rhabdoid morphology that significantly involves the thorax of adults. It has been reported as SMARCA4‐deficient thoracic sarcoma or SMARCA4‐deficient non‐small cell lung carcinoma according to the findings of immunohistochemical and genetic studies. We report a case of thoracic SMARCA4‐UT for which cell block analysis and immunohistochemical staining were useful for the final diagnosis. A 51‐year‐old man had a chief complaint of left back pain and visited our hospital for further examination. Cytological examination of a left pleural effusion was performed and we also made a cell block of the pleural effusion. Cytological examination revealed polyhedral to round tumor cells. The tumor cells appeared singly or formed loosely cohesive clusters. The nuclei were round to oval, enlarged, and sometimes eccentric with prominent nucleoli with irregular borders. The nuclear chromatin was unevenly distributed. The cytoplasm was vacuolar to eosinophilic. There were no characteristic structures of tumor cells. The cell block revealed many single or loosely cohesive round to epithelioid cells. Some tumor cells often exhibited eccentrically located nuclei and lightly eosinophilic cytoplasm, showing a rhabdoid morphology. On immunohistochemistry, the tumor cells were positive for SOX‐2 and they demonstrated significantly reduced SMARCA4 (BRG1) expression; SMARCA2 (BRM) and SMARCB1 (INI1) expression were retained. Accordingly, we made a diagnosis of SMARCA4‐UT. This case demonstrates the importance of performing histological and immunohistochemical analysis using cell blocks for immediate diagnosis.

Three shades of an unusual mediastinal tumour

“…The differences in morphological characteristics between aspiration and exfoliative cytology specimens underscores the importance of considering SMARCA4-UT as a differential diagnosis when working up a discohesive and pleomorphic tumour on effusion cytology, as the classic round to rhabdoid morphology may not be as forthcoming compared to directly sampled tumour cells in aspirates. Cytoplasmic vacuolation of the tumour cells of SMARCA4-UT in effusion specimens has also been reported, 13 presumably a result of the interaction between tumour cells and serous fluid.…”

SMARCB1/INI1‐deficient intrathoracic neoplasm with rhabdoid/plasmacytoid cytomorphology in a patient with plasma cell myeloma: A case report

“…The tumor cells appeared loosely cohesive, with round‐to‐oval nuclei that were enlarged and sometimes eccentric with prominent nucleoli and irregular borders. The cytoplasm was vacuolar to eosinophilic, with epithelioid or rhabdoid morphology 2,14 . Notably, the cytomorphological findings of SMARCB1 (INI1)‐deficient intrathoracic neoplasm might resemble those of SMARCA4‐UT.…”

“…The cytoplasm was vacuolar to eosinophilic, with epithelioid or rhabdoid morphology. 2,14 Notably, the cytomorphological findings of SMARCB1 (INI1)-deficient intrathoracic neoplasm might resemble those of SMARCA4-UT. Thus, IHC for SMARCB1 (INI1) and SMARCA4 (BRG1) is essential for the diagnosis of tumors with undifferentiated epithelioid or rhabdoid cytomorphology.…”

Case report metastatic SMARCB1 (INI1)‐deficient gastric undifferentiated carcinoma in pleural effusion: A case report and literature review

“…A cell block was prepared and immunocytochemical staining was employed, revealing a malignancy without identifiable evidence of differentiation that tested positive for pan‐cytokeratin, BER‐EP4, claudin‐4, and Vimentin, while showing no expression of specific markers of organophilism. Epithelioid sarcoma and thoracic SMARCA4 deficient undifferentiated tumours were considered in the differential diagnosis due to the epithelioid morphology, but eventually epithelioid sarcoma was ruled out as CD34 tested negative, and a thoracic SMARCA4 deficient undifferentiated tumour was ruled out as BRG1 tested positive 6,7 . Additionally, it was discovered that the tumour cells tested negative for p40, and there were no basaloid or plasmacytoid tumour cells observed 8 .…”

“…Epithelioid sarcoma and thoracic SMARCA4 deficient undifferentiated tumours were considered in the differential diagnosis due to the epithelioid morphology, but eventually epithelioid sarcoma was ruled out as CD34 tested negative, and a thoracic SMARCA4 deficient undifferentiated tumour was ruled out as BRG1 tested positive. 6,7 Additionally, it was discovered that the tumour cells tested negative for p40, and there were no basaloid or plasmacytoid tumour cells observed. 8 Furthermore, no significant abnormalities were detected in other organs during the PET-CT scan, particularly in the head and neck region, effectively ruling out the possibility of INI1-deficient sinonasal carcinoma.…”