A case report of SMARCA4/BRG1-deficient non-small cell lung cancer with a spindle cell component found by next-generation sequencing of a brain metastasis

Background: Several studies of different cancers have revealed mutations in switch/sucrose non-fermenting (SWI/SNF) complex genes. Brahma-related gene 1 (BRG1), which is encoded by SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily A, member 4 (SMARCA4), is a member of this complex. SMARCA4/BRG-1-deficient non-small cell lung carcinoma (NSCLC) has been considered a subset of lung cancer that has distinct clinical, pathological, and molecular characteristics, which implies its relationship with SMARCA4/BRG1-deficient thoracic sarcoma. Case presentation: We experienced a case of SMARCA4/BRG1-deficient lung cancer in a 40-year-old female patient with a history of smoking. Magnetic resonance imaging revealed a large mass in the right lung apex with an extension to the extrapulmonary region and cerebral metastasis. Histological analysis showed poorly differentiated carcinoma with spindle cell components. She was diagnosed with NSCLC (stage IV) at that point. An EGFR mutation and ALK and ROS1 rearrangement were not detected, and then treated with chemoradiotherapy. Overall, the tumors were resistant to chemotherapy, and therefore, after 2 years, the brain tumor was excised for histological and molecular analysis. Histologically, the brain mass was an undifferentiated tumor with round cells and glandular components. The mutation in SMARCA4 in the brain specimen was identified by next-generation sequencing. Immunohistochemical examination revealed a complete loss of BRG1. SMARCA4/BRG1-deficient thoracic sarcoma had been raised as a differential diagnosis, collectively, she was diagnosed with SMARCA4/BRG1-deficient NSCLC considering for the result of positivity for cytokeratin AE1/AE3 and claudin-4, and negativity for Sal-like protein 4, CD34, and SRY-box 2 by immunohistochemical examination. Regrettably, a definitive diagnosis required approximately 2 years. She is alive with disease at 30 months after the presentation. Conclusions: The diagnosis of SMARCA4/BRG1-deficient NSCLC is frequently difficult because of no specific morphology and necessity of discrimination from SMARCA4/BRG1-deficient thoracic sarcoma, which is the practical reason this disease is sometimes missed. Immunohistochemistry for BRG1 should be encouraged for the pathological examination of NSCLC with any histology for the prompt and precise diagnosis of SMARCA4/BRG1-deficient NSCLC.