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.