Plasma ctDNA analysis

Plasma to assess the EGFR genotype of circulating ctDNA was collected at baseline and every 1–2 months. The following events were particularly noted: (1) radiological disease progression; (2) clinical disease progression; (3) re-biopsy at disease progression; and (4) treatment change. At each institution, 10-mL samples of blood were centrifuged within 4 hours of plasma collection. Plasma ctDNA was analyzed at SRL Laboratory (Tokyo, Japan) using the cobas® EGFR Mutation Test version 2 (v2) to detect sensitizing EGFR mutations and the T790M resistance mutation.