• Jing Liu, Lei Xia, Yuan Peng, Yu Sheng Huang, and Zhen Zhou Yang.
• Department of Oncology, the Second Affiliated Hospital of Chongqing Medical University, Chongqing, China.
• Medicine (Baltimore). 2021 Oct 1; 100 (39): e27289e27289.

RationaleTransformation 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 metastatic characteristics.Patient ConcernsA 58-year-old male patient was treated with gefitinib (0.25 g /day) as the 1st line treatment due of recurrence after surgical resection for EGFR exon 19 mutation pulmonary adenocarcinoma. However, he experienced recurrence with positive T790 M, and osimertinib (80 mg/day) was administered as the 2nd line therapy.DiagnosisOne year and 6 months after osimertinib initiation, he complained of stomachache, and a diagnostic gastroscopy biopsy confirmed small cell lung cancer in the gastric body, indicating osimertinib-induced phenotypic transformation.Interventions And OutcomesThe patient was treated with etoposide and platinum chemotherapy and maintenance therapy with osimertinib. Finally, the patient achieved a partial response after 4 cycles.LessonsTimely second biopsies should be considered in the diagnosis of phenotypic transformation. After transformation, chemotherapeutic treatment with etoposide and platinum and maintenance therapy with osimertinib inhibited the progression of the disease.Copyright © 2021 the Author(s). Published by Wolters Kluwer Health, Inc.

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