First and repeat rebiopsy for detecting EGFR T790M mutation in non-small-cell lung cancer: CS-Lung-003 prospective observational registry study

Purpose Osimertinib is still essential for the treatment of epidermal growth factor receptor (EGFR)-T790M-positive non-small-cell lung cancer (NSCLC) even in a relapsed setting, which suggests the importance of rebiopsy. The clinical value of repeat rebiopsy in patients with NSCLC who are T790M-negative on a first rebiopsy remains unclear. In this study, we examined the status of the first rebiopsy and evaluated the frequency of repeat rebiopsy of T790M-negative tumors detected by the first rebiopsy. Methods We reviewed 144 patients with NSCLC with major EGFR mutations, but not T790M, who received first- or second-generation EGFR tyrosine kinase inhibitors (TKIs), registered in the prospective, umbrella-type lung cancer patient registry (CS-Lung-003). Results Overall, 63 patients (44%) underwent the first rebiopsy. In the first rebiopsy, 51 (81%) and 12 (19%) of 63 underwent histological/cytological rebiopsy and liquid biopsy with the blood sampling, respectively. In the repeat rebiopsy, 23 (85%) and 4 (15%) of 27 underwent histological/cytological rebiopsy and liquid biopsy, respectively. The most frequently rebiopsied site was a pulmonary lesion (n = 24, 38.7%). Overall, 29 (46.0%) of 63 patients harbored the T790M mutation. Interestingly, a high detection rate of cancer cells did not necessarily indicate a high detection rate of the T790M mutation (p < 0.01). Among 34 patients with T790M-negative tumors confirmed on the first rebiopsy, 20 (58.8%) underwent repeat rebiopsies following interval therapy, revealing that seven (36.8%) had T790M-positive tumors. Osimertinib yielded median progression-free survival of 11.8 and 16.2 months in patients with the 790M mutation detected by the first rebiopsy and repeat rebiopsy, respectively. Conclusion In our prospective cohort, the T790M mutation was detected in 46% of patients who underwent the first rebiopsy. Repeat rebiopsy may increase the ability to detect the T790M mutation positivity rate.