Takeda Y, Naka G, Yamaguchi Y, et al. - Researchers explored the clinical features of EGFR (epidermal growth factor receptor)-mutated lung cancer patients with the T790M substitution resistant to EGFR-tyrosine kinase inhibitors. They also investigated the benefits of rebiopsy as well as liquid biopsy for these patients. This study involved 113 patients found to have EGFR mutations after being screened. The patients were suspected to harbor the T790M substitution if they exhibited an EGFR exon 19 deletion, had a new lesion, and were given gefitinib as first-line treatment. The usefulness of repeated tissue or liquid biopsies was evident in maximizing the detection rate of the T790M substitution in patients with positive factors related to the T790M mutation. In patients with coexisting original mutations, brain metastases, tumor enlargement by ≥12 mm, or metastases at minor sites, the T790M substitution was detected through rebiopsy. To attenuate “detection overlook” in such patients, it is required that these biopsies are repeated numerous times.