Complex Germline K757N Mutation in Non-Small-Cell Lung Cancer: A Case Report

Epidermal growth factor receptor (EGFR) mutations are usually oncogenic drivers of lung tumor development and progression. While common sensitizing mutations respond well to targeted therapy, the relevance of germline EGFR mutations is less clear. We describe a 65-year-old, previously healthy, male diagnosed with non-small-cell lung cancer. Familial history for lung cancer is negative. Targeted next-generation sequencing on the tumor biopsy sample revealed an atypical EGFR K757N mutation at 50% allele frequency and genetic review of a previously acquired gastric sample confirms the mutation as a germline change. He received standard first-line chemoimmunotherapy with carboplatin, pemetrexed, and pembrolizumab, and after 8 months therapy continues, with stable disease, to receive maintenance pemetrexed and pembrolizumab. To our knowledge, this is the first report of an atypical, germline K757N EGFR mutation. While the clinical relevance of this mutation is unclear, standard reporting of the allelic frequency of novel, atypical mutations can detect potential germline changes.