Incidence of T790M mutation in (sequential) rebiopsies in EGFR -mutated NSCLC-patients

Abstract Aim Non-small cell lung cancer (NSCLC)-patients with an epidermal growth factor receptor ( EGFR )-mutation have median progression-free survival (PFS) of 12 months on tyrosine kinase inhibitors (TKIs). Resistance is mediated by the EGFR T790M-mutation in the majority of patients. Longitudinal follow-up data are lacking. We retrospectively evaluated EGFR -mutated NSCLC-patients who were rebiopsied after TKI-treatment. A subgroup was sequentially rebiopsied along the course of the disease. Patients and methods Advanced EGFR -mutated NSCLC-patients who had both a pre-TKI biopsy and post-TKI biopsy available were included. Information on treatments and (re)biopsies was collected chronologically. Primary endpoint was the incidence of the T790M-mutation. Results Sixty-six patients fulfilled the inclusion criteria. In first post-TKI biopsies, T790M-mutation was detected in 34 patients (52%) of patients. Twenty-seven patients had subsequent post-TKI rebiopsies with mutation analysis available; in 10 patients (37%) the T790M-status in subsequent post-TKI rebiopsies was not consistent with the T790M-status of the first post-TKI biopsy. Progression free survival (PFS) on TKI-treatment was 12.0 months. Objective response rate on TKI-treatment was 81%. Patients developing T790M-mutation at post-TKI biopsy had longer median PFS compared to T790M-negative patients (14.2 versus 11.1 months respectively ( P = 0.034)) and longer overall survival (45.9 months versus 29.8 months respectively ( P = 0.213)). Transformation to SCLC was detected in 1 patient (2%). Conclusion Incidence of T790M-mutation at first post-TKI biopsy in this cohort of EGFR -mutated NSCLC-patients was 52%. Detection of T790M-mutation was not consistent over time; some patients who were T790M-positive at first post-TKI biopsy became T790M-negative in later post-TKI rebiopsies and vice versa. T790M-positive patients showed longer PFS than T790M-negative patients. Whether the low incidence of transformation to SCLC is justifying post-TKI rebiopsy in EGFR -mutated NSCLC-patients with acquired TKI-resistance in regular clinical practice is debatable.