Fine needle aspiration cytology of metastatic SMARCA4-deficient sinonasal teratocarcinosarcoma: First report in literature

Inactivating mutations of SMARCA4 and accompanying loss of BRG1 immunoexpression were recently identified in majority of sinonasal teratocarcinosarcomas (TCS). These rare and aggressive neoplasms have potential for nodal metastasis, presenting opportunities for diagnosis on fine needle aspiration cytology (FNAC). However, their cytological features have not been described till date. A 22-year-old male was diagnosed to have SMARCA4-deficient TCS on a nasal mass biopsy, and was started on neoadjuvant chemotherapy. Four months later, FNAC from cervical lymph nodes showed predominantly discohesive tumor cells with moderate to abundant cytoplasm and enlarged vesicular nuclei with prominent nucleoli. Occasional cohesive fragments showed ovoid to spindled tumor cells attached to fibrovascular cores. Few loosely cohesive cells with scant cytoplasm and nuclei having stippled chromatin, and rhabdoid cells were also seen. Frequent mitoses, apoptosis and nuclear streaking were evident. Overt squamous or glandular differentiation was absent. Tumor cells showed loss of BRG1 immunostaining and beta-catenin immunopositivity on a cell block, consistent with metastatic SMARCA4-deficient TCS. The diversity of cell types in SMARCA4-deficient TCS can result in a broad spectrum of cytological features that overlap with that of other regional metastatic tumors including neuroendocrine carcinoma, olfactory neuroblastoma and melanoma. Further, all components of TCS as seen in the primary tumor may not be present in nodal metastases. Thus, SMARCA4-deficient TCS should be considered in the differential diagnosis of metastatic poorly/undifferentiated malignancies in cervical lymph node aspirates, and appropriate ancillary tests viz. BRG1 immunostaining employed for accurate diagnosis.