Lung Adenocarcinoma Patient Harboring EGFR -KDD Achieve Durable Response to Afatinib: A Case Report and Literature Review.

The rapid development of epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) has revolutionized the treatment of patients with advanced or metastatic non-small cell lung cancer (NSCLC) harboring mutations including but not limited to exon 19 deletions (19 del) and point mutation L858R in exon 21. However, the efficacy of EGFR-TKIs in patients with rare mutations, such as kinase domain duplication (KDD), remains elusive. -KDD often results from in-frame tandem duplication of exons 18-25, causing subsequent constitutive activation of EGFR signaling. Several case reports have revealed the efficacies of EGFR-TKIs in advanced lung adenocarcinoma (LUAD) with -KDD but yielded variable antitumor responses. In the present study, we report a 61-year-old male patient diagnosed with T1N3M0 (stage IIIB) LUAD harboring -KDD involving exons 18-25. He was treated with afatinib and achieved partial response (PR) with progression-free survival (PFS) of 12 months and counting. Our work, confirming -KDD as an oncogenic driver and therapeutic target, provides clinical evidence to administer EGFR-TKIs in patients with advanced LUAD harboring -KDD.