Purpose: To assess the role of pathologic complete response (pCR) after neoadjuvant therapy as surrogate end point of disease-free survival (DFS) and overall survival (OS) in patients with breast cancer, we performed a trial-based meta-regression of randomized studies comparing different neoadjuvant systemic treatments., Methods: The systematic literature search included electronic databases and proceedings of oncologic meetings. Endocrine therapy trials were excluded. Treatment effects on DFS and OS were expressed as hazard ratios (HRs), and treatment effects on pCR were expressed as odds ratios (ORs). A weighted regression analysis was performed on log-transformed treatment effect estimates to test the association between treatment effects on the surrogate outcome and treatment effects on the clinical outcome., Results: Twenty-nine trials, 59 arms, and 30 comparisons, for a total of 14,641 patients, were included in the analysis. Using the complete set of data, the regression of either the log(HR) for DFS or the log(HR) for OS on the log(OR) for pCR demonstrated only weak associations (R(2) = 0.08; 95% CI, 0 to 0.47; and R(2) = 0.09; 95% CI, 0.01 to 0.41, respectively). Better associations were found in an exploratory analysis assessing a subset of trials comparing intensified/dose-dense chemotherapy versus standard-dose regimens (DFS: R(2) = 0.79; 95% CI, 0.26 to 0.95; P = .003; and OS: R(2) = 0.57; 95% CI, 0.19 to 0.93; P = .03)., Conclusion: This meta-regression analysis of 29 heterogeneous neoadjuvant trials does not support the use of pCR as a surrogate end point for DFS and OS in patients with breast cancer. However, pCR may potentially meet the criteria of surrogacy with specific systemic therapies., (© 2014 by American Society of Clinical Oncology.)