Small cell carcinoma presenting with massive pleural spread mimicking malignant pleural mesothelioma

Small cell carcinoma (SCC) predominantly spreading over the pleura is exceedingly rare and difficult to diagnose without proof of malignant effusion. A 65-year-old man presented with right pleural thickening and effusion and was diagnosed with SCC based on a thoracoscopic pleural biopsy. He received combined chemotherapy consisting of cisplatin and irinotecan hydrochloride, which resulted in a complete response. Seven months later, local relapse was observed. Thereafter, he received second-, third- and fourth-line chemotherapies and died of tumor progression 21 months after the diagnosis. Considering the possibility of SCC with pleural spread, performing early invasive procedures is important for diagnosing pleural malignancies.