Small-cell lung carcinoma transformation of lung adenocarcinoma diagnosed by pericardial effusion: A case report.

The present report describes a case of a 68-year-old male patient with epidermal growth factor receptor (EGFR)-mutant non-small cell lung carcinoma (NSCLC). After cytotoxic chemotherapy of three regimens following 22 months of treatment with EGFR-tyrosine kinase inhibitors (EGFR-TKIs), including osimertinib, the patient underwent S-1 treatment. Despite a decrease in carcinoembryonic antigen 1 month after initiating S-1 treatment, the patient developed cardiac tamponade. The evaluation of pericardial effusion confirmed small-cell lung carcinoma (SCLC) transformation. Subsequently, a combination therapy of carboplatin and etoposide was administered, which led to a marked improvement in imaging. In patients with NSCLC who develop pericardial effusion after long-term EGFR-TKI therapy, including osimertinib treatment, it is important to investigate whether SCLC transformation occurs or not as a treatable entity.