Cytomorphologic features of SMARCA4-deficient non-small cell lung carcinoma and correlation with immunohistochemical and molecular features

BACKGROUND SMARCA4/BRG1-deficient tumors and those that have loss of SMARCA/BRG1 have been described as various aggressive carcinomas and sarcomas, including a subset of non-small cell lung carcinoma (NSCLC). Cytomorphologic features of NSCLCs are yet to be described. The objective of this study was to evaluate the cytomorphologic features, immunohistochemical profile, and molecular profile of SMARCA4/BRG1-deficient NSCLC (SMARCA4-dNSCLC). METHODS The authors retrospectively searched for cases with SMARCA4/BRG1 functional loss alterations, which were identified in molecular studies and further confirmed by immunocytochemistry, and they reviewed the cytomorphologic features. Tumors with BRG1 loss were also stained with an extensive antibody panel. Molecular profiling and clinical information of the identified cases were scrutinized. RESULTS In total, 12 cytopathology cases from different anatomic sites were included. All cases showed variable expression of cytokeratin irrespective of type. One-half of cases had glandular features, followed by squamoid features, and poorly differentiated features. The most common cytologic features included sheets or papillary architecture, round or oval cell shapes, nuclear enlargement, moderate-to-marked pleomorphism, and coarse chromatin. Two cases with poorly differentiated cytomorphology had a predominance of single cells, scant cytoplasm, and macronucleoli. Variable expression of epithelial markers was noted in all cases. TP53 was the most frequently co-mutated gene in SMARCA4-dNSLCs. CONCLUSIONS This study demonstrates that SMARCA4-dNSCLCs can have a wide spectrum of cytomorphologic features, ranging from a relatively well differentiated adenocarcinoma to a poorly differentiated/undifferentiated carcinoma, with the majority of cases exhibiting some high-grade features, such as mitosis, apoptosis, necrosis, and marked pleomorphism.