Gastric Metastasis and Transformation of Primary Lung Adenocarcinoma to Small Cell Cancer After Acquired Resistance to EGFR-TkIs: A Case Report

Abstract Background: Transformation to small cell lung cancer (SCLC) is one of the mechanisms of resistance to epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs). However, no standard treatment is available after the transformation. In addition, gastric metastasis of primary lung cancer is rarely observed, thus, little is known about its metastasis characteristics. Case presentation: A 58-year-old male patient was treated with osimertinib (80 mg/day) as the 2st line treatment due to recurrence and metastasis after surgical resection first-line gefitinib for EGFR exon 19 mutation pulmonary adenocarcinoma. 1 year and 3 months after osimertinib initiation, all the lesions are increased. He complained stomachache, and a diagnostic gastroscopy biopsy confirmed small cell lung cancer in the gastric body, indicating osimertinib-induced phenotypic transformation. He was treated with etoposide and los platinum chemotherapy and the maintenance therapy with osimertinib. Finally, the patient achieved a partial response after four cycles. Conclusions: Timely second biopsy should be valued in the diagnosis of phenotypic transformation. After transformation, a chemotherapeutic treatment with etoposide and platinum and maintenance therapy with osimertinib inhibited the progress of the disease.