A Study to Assess the Efficacy and Safety of Firmonertinib Versus Placebo for Adjuvant Treatment in Participants With Stage IB - IIIB NSCLC With Uncommon Epidermal Growth Factor Receptor (EGFR) Mutations, Following Complete Surgical Resection With or Without Adjuvant Chemotherapy（FIRMOST）

This is a Phase 3, global, double-blind, randomized, controlled multicenter clinical study to assess the efficacy and safety of adjuvant treatment with firmonertinib versus placebo in participants with Stage IB-IIIB NSCLC with uncommon EGFR mutations (exon 20 insertions, PACC and classical-like mutations) after complete surgical resection with or without adjuvant chemotherapy. About 338 eligible participants will be enrolled and randomized in a 1:1 ratio to receive either firmonertinib 240 mg QD or placebo QD in 21-day treatment cycles. Before randomization, the participant must have undergone complete surgical resection (R0 resection), must have sufficiently recovered from surgery, and must have completed adjuvant chemotherapy (if applicable). The participants will receive firmonertinib or placebo as adjuvant treatment until unacceptable toxicity, withdrawal of informed consent, disease recurrence, initiation of new antitumor treatment, completion of treatment, or other end of treatment reason is met.