LAUSR

SummarySmall-cell lung cancer (SCLC) combined with epidermal growth factor receptor (EGFR) mutations is extremely rare, and standard chemotherapeutic strategies have not yet been established. In the present study, we report a case of a 67-year-old man who presented with combined SCLC with EGFR mutation (exon 19 deletion). Systemic chemotherapy with cisplatin and irinotecan was initiated as first-line chemotherapy, and computed tomography findings revealed tumor shrinkage after two cycles of chemotherapy. However, after the third cycle of the treatment, disease progression was observed including the appearance of pleural and pericardial effusion. Cytologic examination of pleural and pericardial effusion revealed adenocarcinoma and no characteristics of SCLC, and an EGFR mutation was detected, in line with the initial diagnosis. Afatinib was then administered as second-line chemotherapy, which resulted in a partial response that lasted for 6 months. Re-biopsy after resistance to first-line chemotherapy suggested that the adenocarcinoma component harboring the EGFR mutation became dominant in association with disease progression, and afatinib provided clinical efficacy as second-line chemotherapy.