<i>MET</i> and <i>NF2</i> alterations confer primary and early resistance to first‐line alectinib treatment in <i>ALK</i>‐positive non‐small‐cell lung cancer

Although first-line alectinib has prolonged survival in ALK-mutated non-small-cell lung cancers (NSCLCs), the response to treatment varies among patients, and the primary/early development of alectinib resistance mechanisms is still not fully understood. Here, we analyzed molecular profiles of 108 alectinib-treated patients (first-line and second-line after crizotinib) with confirmed relapse by targeted sequencing of cancer-related genes. After first-line treatment, off-target MET and NF2 alterations were more frequent than on-target alterations within the first 6 months, causing primary or early resistance. Conversely, on-target alterations became prevalent after 1 year of first-line alectinib treatment and predominantly after second-line. The incidence of acquired resistance also depended on EML4-ALK variants. In variant 1 (v1), off-target alterations were responsible for 50% of resistance cases after first-line alectinib therapy, whereas on-target mutations had no contribution in this subgroup. In variant 3 (v3), on-target alterations resulted in 46% of resistance cases, whereas only 18% were caused by off-target mutations. After second-line treatment, the most common mutations in v1 were L1196M (42%) and G1269A (25%), while G1202R was detected in 45% of v3 tumors. These findings emphasize the importance of stratifying resistance mechanisms to guide tailored treatment for ALK-positive NSCLCs.