The emergence of T790M mutation in EGFR-mutant lung adenocarcinoma patients having a history of acquired resistance to EGFR-TKI: focus on rebiopsy timing and long-term existence of T790M

Different growth kinetics occurring between the sensitive and T790M-containing cells may result in the repopulation of tumor cells over time. Little information has yet been uncovered on whether rebiopsy timing influences the T790M detection rate. We enrolled a total of 98 epidermal growth factor receptor (EGFR)-mutant lung adenocarcinoma patients, who had a history of acquired resistance to EGFR-tyrosine kinase inhibitor (TKI) and available rebiopsy tumor specimens for reassessment of EGFR mutations. Rebiopsy was performed at the time of first EGFR-TKI progression in 54 patients (55.1%); for the other 44 patients (44.9%), rebiopsy was done with an interval from first EGFR-TKI progression (median 470.5 days, range 46-1742 days). Our results indicated that rebiopsy timing did not influence the detection rate of T790M and that the mutation could be identified in patients with a long EGFR-TKI-free interval. For patients without suitable lesions for rebiopsy at the time of EGFR-TKI progression, an attempt to rebiopsy should be considered during the subsequent treatment courses.