EGFR-Mutated Lung Adenocarcinoma Successfully Treated With Osimertinib After Spontaneous Transformation to SCLC and Adenocarcinoma With Neuroendocrine Differentiation: Case Report

Lineage transformation from lung adenocarcinoma (LUAD) to SCLC is associated with resistance to EGFR tyrosine kinase inhibitors. In addition to loss of p53 and RB, transformed SCLCs are usually not dependent on EGFR signaling, which renders the tumors unresponsive to EGFR tyrosine kinase inhibitors. Here, we present a case of spontaneous transformation from EGFR-mutant LUAD with loss of p53 and RB to EGFR expression-positive SCLC and neuroendocrine-differentiated LUAD, which was successfully treated with osimertinib.