EGFR-Mutant Non-Small Cell Lung Cancer in the Era of Precision Medicine: Importance of Germline EGFR T790M Testing.

With the rapid development of precision medicine, next-generation sequencing (NGS) has provided the ability to uncode tumors at the DNA level. Identifying EGFR mutations and other molecular changes has become more crucial in the management of non-small cell lung cancer (NSCLC) than ever before. Although the histologic subtypes in patients with advanced NSCLC remain valid in determining treatment options, the detection of specific molecular signatures such as de novo T790M with sensitizing EGFR mutations could be more useful than the histologic subtype itself. Germline T790M mutation should be suspected and tested for when multiple biopsies show de novo T790M mutations or when de novo T790M is found in patients with a family history of lung cancer. This case report presents a 60-year-old woman with bilateral NSCLC with 3 different distinct histologic diagnoses. Evaluating the molecular profile using NGS completely changed the diagnosis, prognosis, and management of this rare presentation of NSCLC.