An EGFR-mutated Lung Adenocarcinoma Undergoing Squamous Cell Carcinoma Transformation Exhibited a Durable Response to Afatinib.

Squamous cell carcinoma (SCC) transformation has been identified as a mechanism of resistance to first-generation epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs), gefitinib or erlotinib, in EGFR-mutated lung cancer. However, whether second- or third-generation TKIs can overcome resistance due to SCC transformation remains unclear. We herein report an EGFR-mutated lung adenocarcinoma undergoing transformation into SCC that exhibited a durable response to afatinib, which is a second-generation irreversible EGFR-TKI. We suggest that afatinib can be considered as a treatment option for EGFR-mutated tumor undergoing SCC transformation, particularly in the absence of a T790M mutation. Clinical Practice Point Afatinib can be considered an option for EGFR-mutated tumor undergoing squamous cell carcinoma transformation.