Epidermal Growth Factor Receptor Kinase Domain Duplication in Lung Adenocarcinoma with Response to Osimertinib: A Case Report and Literature Review.

Introduction: Liquid and tissue next-generation sequencing (NGS) are both important in oncological care. We report a case of metastatic non-small cell lung adenocarcinoma (NSCLC) with a rare epidermal growth factor receptor kinase domain duplication (EGFR-KDD) identified on liquid biomarker testing which led to sustained targeted treatment.

Case presentation: A 54-year-old male was diagnosed with metastatic NSCLC and progressed on multiple lines of therapies: carboplatin-pemetrexed-pembrolizumab, cisplatin-docetaxel, and durvalumab-tremelimumab over a 6-month period. Liquid NGS identified a rare EGFR-KDD mutation that was treated with osimertinib leading to 5 months of progression-free survival and significant clinical improvement before ultimately opting for hospice due to intolerance with osimertinib.

Conclusion: Liquid and tissue NGS should be used in combination to guide treatment and monitor treatment response. Osimertinib may be particularly effective in metastatic NSCLC with EGFR-KDD mutations.