• Kazuhiro Usui, Takuma Yokoyama, Go Naka, Hiroo Ishida, Kazuma Kishi, Kohei Uemura, Yasuo Ohashi, and Hideo Kunitoh.
• NTT Medical Center, Shinagawa, Tokyo, Japan.
• Jpn. J. Clin. Oncol. 2019 Jun 1; 49 (6): 554-558.

BackgroundOsimertinib, a third generation epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor (TKI), is active against EGFR-mutant non-small cell lung cancer (NSCLC) resistant to first-/second-generation EGFR-TKIs with the T790M mutation. T790M monitoring in plasma circulating tumor DNA (ctDNA) in patients receiving EGFR-TKIs is less invasive than re-biopsy and could provide valuable clinical information.MethodsPatients with advanced or postoperative recurrent NSCLC with sensitizing EGFR mutations who were planned to receive or were receiving first-/second-generation EGFR-TKI treatment without disease progression were eligible for enrollment. Plasma samples at baseline and every 1-2 months thereafter were analyzed for EGFR mutation status using the cobas®EGFR Mutation Test v2.ResultsBetween September 2016 and March 2017, 122 patients at 15 Japanese institutions were enrolled. In August 2018, 1291 plasma samples from 121 patients were analyzed for EGFR mutation status. At baseline, a sensitizing EGFR mutation was detected in 29 (23.9%) of 121 patients and T790M mutation was detected in three (2.5%). At follow-up, 66 (54.5%) patients experienced disease progression and 64 (52.9%) discontinued first-line EGFR-TKI treatment. Twenty-two (18.2%) patients showed T790M in plasma ctDNA, of which 15(68.2%) received osimertinib. Although 31 patients received re-biopsy to examine EGFR status at disease progression, T790M was detected in only nine (22.0%) patients, of which 7 (77.8%) received osimertinib.ConclusionsctDNA monitoring during EGFR-TKI treatment is useful for detecting T790M mutation. The efficacy of osimertinib treatment based on T790M status in plasma ctDNA remains to be established, warranting further research.© The Author(s) 2019. Published by Oxford University Press.

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