A Case of Combined Small Cell Lung Carcinoma with a Rhabdomyosarcomatous Component Diagnosed by a Thoracoscopic Biopsy and Treated with Chemoimmunotherapy.

A 75-year-old woman presented with left pleural effusion and pleural nodules. A computed tomography-guided percutaneous biopsy suggested rhabdomyoblastic differentiation; however, a definitive diagnosis could not be established. A subsequent thoracoscopic biopsy revealed combined small cell lung carcinoma (C-SCLC) with a rhabdomyosarcomatous component. Small cell carcinoma cells were positive for pancytokeratin, chromogranin A, and synaptophysin, whereas rhabdomyosarcomatous cells were positive for desmin and myogenin. Chemoimmunotherapy with carboplatin, etoposide, and atezolizumab resulted in a remarkable tumor response. This is an extremely rare case of C-SCLC with rhabdomyosarcomatous differentiation that was diagnosed using a thoracoscopic biopsy and was treated with chemoimmunotherapy.