Background: Cancers with activating EGFR mutations are exquisitely sensitive to EGFR tyrosine kinase inhibitors (TKIs) and retrospective data suggests adjuvant TKIs may improve outcomes in EGFR mutants. This prospective trial investigates the safety and efficacy of adjuvant erlotinib in EGFR mutation-positive NSCLC. Methods: Patients (pts) with surgically resected stage IA-IIIA NSCLC harboring activating EGFR mutations were treated with 150 mg/day of erlotinib for 2 years (y) after completion of any standard adjuvant chemotherapy and/or radiotherapy. The trial was designed to enroll 36 patients, and powered to demonstrate a primary endpoint of 2 y disease free survival (DFS) exceeding 85%, which would suggest improvement over the historically expected 70% 2 y DFS in early stage EGFR-mutant NSCLC (J Thorac Oncol 6:569). Results: Thirty-six pts were enrolled at five sites between 1/08 and 11/09; 53% stage I; 19% stage II; 28% stage IIIA. Toxicities were typical of erlotinib; no grade 4 or 5 events or pneumonitis occurred. 8 pts (22%) required one dose reduction to 100 mg/day and 5 (14%) two reductions to 50 mg/day for grade 3 or persistent grade 2 toxicities. 11 pts discontinued before 2 full years (<1 month (mo) [4], 1-12 mo [2] and 12-23 mo [5]) for toxicities [6], patient preference [3], prostate cancer [1] and recurrence [1]. After a median follow-up of 2.5 y, the 2 y DFS from enrollment is 94% (95% CI 80%, 99%). 10 patients have recurred, 1 during erlotinib treatment and the others after stopping erlotinib (interval before recurrence 2 mo [1], 6-12 mo [4], >12 mo [4]). Genotyping on repeat biopsies from seven of the recurrent cases is underway, as is assessment of response to subsequent erlotinib therapy. Two pts have died of recurrence: one at 1.5 y who stopped erlotinib after 1 mo for toxicity, and one at 2 y who progressed while on erlotinib. Conclusions: This is the first prospective study to report the efficacy of adjuvant erlotinib in NSCLC pts with EGFR mutations. This approach is feasible and yields excellent 2y DFS compared to historical genotype-matched controls. This trial was subsequently expanded to 100 pts to permit subgroup analysis by stage.