Mixed response to osimertinib and the beneficial effects of additional local therapy

Background Although non‐small cell lung cancers (NSCLCs) harboring EGFR mutations initially respond well to EGFR‐tyrosine kinase inhibitors (TKIs), they typically progress after approximately one year. The EGFR T790M mutation is the most common resistance mechanism. NSCLCs with T790M respond well to osimertinib; however, the heterogeneity of NSCLCs may limit the efficacy. Some patients exhibit a mixed response (MR), in which some lesions shrink and others progress, but little is known of the incidence and characteristics of such a response. We sought to determine the frequency and clinical course in MR patients.