RESUMEN
BACKGROUND: Several patients treated with osimertinib experience progressive disease. The aim was to clarify the mechanisms underlying resistance to osimertinib. METHODS: ELUCIDATOR: A multi-centre, prospective, observational study involved chemotherapy-naive patients with advanced non-small cell lung cancer receiving osimertinib. Mutations in cancer-associated genes, detected via ultrasensitive next-generation sequencing of circulating tumour deoxyribonucleic acid samples, were collected at baseline and after progressive disease detection. These paired plasma samples were compared. RESULTS: Of 188 patients enrolled (May 2019-January 2021), 178 (119 females [67 %]) median age 74 years, were included. Patients, n = 95 (53 %) had epidermal growth factor receptor exon 19 deletion mutations. Among 115 patients with progressive disease, circulating tumour deoxyribonucleic acid levels of 85 patients were analysed. MET amplification (n = 4), TP53 mutations (n = 4), PIK3CA mutations (n = 3), BRINP3 mutation (n = 2), BRAF mutation (n = 2), APC mutation (n = 1), RET mutation (n = 1) and epidermal growth factor receptor (EGFR) resistance mutation, and C797S (n = 1) were detected. Patients with baseline TP53 mutations, with MET or EGFR amplification had shorter progression-free (PFS) and overall survival. Patients with PIK3CA mutations tended to shorter PFS. CONCLUSION: MET amplification and PIK3CA mutation mechanisms underly resistance to osimertinib in patients. Patients with coexisting mutations or amplifications at baseline had shorter PFS and overall survival.