Histologic transformation from adenocarcinoma to both small cell lung cancer and squamous cell carcinoma after treatment with gefitinib

RATIONALE: In the past decade, epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) treatment had been an important therapy for treating advanced EGFR-mutated lung cancer patients. However, a large number of these patients with EGFR-TKIs treatment always acquired resistance to these drugs in one year. The histologic transformation is an important resistance mechanism. PATIENT CONCERNS: Here we reported a 41-year-old man with EGFR-mutated lung adenocarcinoma and he showed histologic transformation to both small-cell lung cancer (SCLC) and squamous cell carcinoma (SCC) after treatment of gefitinib. DIAGNOSES: A case of EGFR-mutated lung cancer. INTERVENTIONS: Medical thoracoscopy examination was performed and the patient was diagnosed as a EGFR-mutated lung adenocarcinoma. Then gefitinib was administered orally at a dose of 250 mg daily. The patient received treatment with chemotherapy (etoposide 0.1 g day 2-5 + cis-platinum 30 mg day 2-4) after acquiring resistance to gefitinib. OUTCOMES: The patient died in April 2017 that survived for 32 months from lung cancer was found for the first time. LESSONS: To the best of our knowledge, it is the first case of EGFR-mutated lung adenocarcinoma transforming to both SCLC and SCC which was treated with and responded to gefitinib.