• Tao Zhou, Qiang Xiong, Chen Hong, Qian Wang, Wenxian Wang, Chunwei Xu, Jing Cai, and Yangtze River Delta Lung Cancer Cooperation Group.
• Department of Oncology, The Second Affiliated Hospital of Nanchang University, Nanchang, China.
• Medicine (Baltimore). 2022 Aug 26; 101 (34): e30269.

RationaleUncommon epidermal growth factor receptor (EGFR) mutations are increasingly being identified in non-small cell lung cancer. Insertion and deletion mutations have been detected in exons 18, 19, and 20, but not in exon 21. In patients with uncommon mutations, the second-generation EGFR tyrosine kinase inhibitor afatinib has shown good efficacy, whereas that of dacomitinib, another second-generation EGFR-tyrosine kinase inhibitor, remains unknown. Here, we reported a patient with a novel EGFR21 exon insertion-deletion (indel) mutation and demonstrated the efficacy of dacomitinib.Patient ConcernsA 59-year-old nonsmoking Chinese male was admitted to the hospital with lung cancer after a chest computed tomography for coughing and sputum. The patient's condition progressed after multiple treatments including surgery, chemotherapy, and radiotherapy.DiagnosisThe patient had clinical manifestations of cough and sputum and was pathologically confirmed to have T2bN1M0 (stage IIB) lung adenocarcinoma according to the seventh edition of tumor-node-metastasis staging. The patient underwent a second operation after detection of recurrence, and postoperative pathology confirmed adenocarcinoma of the lung. The patient progressed again after surgery, and the tumor-node-metastasis stage was changed to T4N0M1a (stage IVA) before treatment with dacomitinib.InterventionsAfter detection of the EGFR exon 21 indel mutation, the patient began treatment with dacomitinib (45 mg once a day) on March 12, 2021.OutcomesAfter 1 month of targeted therapy, the patient showed a partial response to dacomitinib. As of March 19, 2022, his condition remained stable and he continued to receive dacomitinib. Progression-free survival reached 12.4 months. The patient experienced mild adverse reactions of pruritus during the use of dacomitinib, but recovered after drug treatment.LessonWe reported a novel EGFR exon 21 indel mutation in a lung adenocarcinoma patient. Dacomitinib showed efficacy in the treatment of a patient with this mutation, suggesting that its efficacy in patients with uncommon mutations should be explored further. The next-generation sequencing is recommended as a guiding tool for the treatment of advanced non-small cell lung cancer.Copyright © 2022 the Author(s). Published by Wolters Kluwer Health, Inc.

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