“Heterogeneity of treatment effect on patients’ long-term outcome according to pathological response type in neoadjuvant RCTs for breast cancer.”

Introduction: To provide evidence explaining the poor association between pCR and patients’ long-term outcome at trial-level in neoadjuvant RCTs for breast cancer (BC), we performed a systematic-review and meta-analysis of all RCTs testing neoadjuvant treatments for early-BC and reporting the hazard ratio of DFS (HRDFS) for the intervention versus control arm stratified by pathological response type (i.e., pCR yes versus no). Methods: The objective was to explore differences of treatment effects on DFS across patients with and without pCR. We calculated the pooled HRDFS in the two strata of pathological response (i.e., pCR yes versus no) using a random-effects model, and assessed the difference between these two estimates using an interaction test. Results: Ten RCTs and 8496 patients were included in the analysis. Patients obtaining pCR in the intervention-arm had a higher, although not statistically significant, risk of DFS-event as compared with patients obtaining pCR in the control-arm: the pooled HRDFS for the experimental versus control arm was 1.23 (95%CI, 0.91–1.65). On the opposite, the risk of DFS-event was higher for control as compared with the intervention-arm in the stratum of patients without pCR: the pooled HRDFS was 0.86 (95%CI, 0.78–0.95). Treatment effect on DFS was significantly different according to pathological response type (interaction test p: 0.014). Conclusion: We reported new evidence that contributes to explaining the poor surrogacy value of pCR at trial-level in neoadjuvant RCTs for early-BC.