Cavitation and durable remission in a PD-L1-positive, TP53-mutant SMARCA4-deficient lung tumor following immunochemotherapy and radiotherapy: A case report.

SMARCA4-deficient undifferentiated tumors (SMARCA4-UTs) are rare, aggressive thoracic malignancies with dismal prognosis. Most cases are refractory to conventional therapy, a significant number of patients show no response to one or more chemotherapy regimens, exhibiting an overall survival (OS) of less than six months. We report a case of a 52-year-old male heavy smoker with a right lower lobe SMARCA4-UTs harboring TP53 mutation and PD-L1 expression (tumor proportion score [TPS] 30%, combined positive score [CPS] 30%). The tumor showed loss of SMARCA4 (also known as BRG1), high Ki-67 (∼50%), and rapid growth. After six cycles of tislelizumab + paclitaxel/cisplatin, the lesion demonstrated partial remission and progressive cavitation on CT imaging. Consolidative radiotherapy (60 Gy/30 fractions) further reduced the tumor burden. The survival period of this patient was 17 months long. This case highlights that PD-L1 expression and radiologic cavitation may serve as potential efficacy biomarkers in SMARCA4-UTs, even in tumors with TP53 mutations and a high proliferative index. Combined immunotherapy with chemotherapy and radiotherapy may confer durable disease control in this aggressive lung cancer subtype.