579 Background: The Katherine trial reported a 3-year invasive disease-free survival (DFS) of 77% in patients not achieving pathological complete response (pCR) and continuing on adjuvant trastuzumab. Case series suggest better outcomes and data support that some patients with residual disease have similar outcomes to those with pCR (Steenbruggen et al). The absolute benefit of adjuvant trastuzumab emtansine (T-DM1) would be smaller in patients with favourable outcomes despite residual disease. As such, a more precise estimate of 3-year DFS is needed for treatment planning. Methods: We reviewed reports of randomized trials of neoadjuvant chemotherapy and HER2-directed therapy and extracted the 3-year DFS, a validated surrogate endpoint in HER2-positive early-stage breast cancer. Data were extracted for patients with residual disease and with pCR. The mean 3-year DFS weighted by study sample size was calculated. Meta-regression comprising linear regression weighted by sample size (mixed effects) was performed to explore associations between 3-year DFS and trial-level patient, disease and treatment factors and changes in 3-year DFS over time. Quantitative significance was explored using methods described by Burnand et al. Results: Eleven studies comprising 3908 patients were included in the analysis. The mean 3-year DFS for patients with pCR and for residual disease was 90.1% and 80.0%, respectively. DFS improved over time. For trials whose final year of accrual was after 2010, mean 3-year DFS for residual disease was 84.7% compared to 78.0% for trials completing accrual before that time (p