Tailoring post-neoadjuvant staging to tumor biology: A comparison of Neo-Bioscore, RCB, and pathologic stage in a Latin American cohort.

Abstract

e12628 Background: Selecting the optimal staging system to guide adjuvant escalation after neoadjuvant chemotherapy (NAC) remains a clinical challenge. Validated models like the AJCC Pathologic Stage (PS), Residual Cancer Burden (RCB), and Neo-Bioscore (NB) often yield conflicting results when applied to diverse populations. In Latin America, where patients frequently present with locally advanced disease, the real-world performance of these tools is largely undocumented. We evaluated whether the prognostic value of PS, RCB, and NB varies by immunophenotype in this population, aiming to align risk assessment with tumor biology. Methods: We analyzed a retrospective cohort of 850 patients with stage I–III breast cancer treated with NAC and surgery at a tertiary cancer center in Mexico (2010–2020). The cohort included 593 (69.8%) Luminal, 171 (20.1%) Triple-Negative (TNBC), and 86 (10.1%) HER2-enriched tumors. Prognostic performance for 10-year Disease-Free Survival (DFS) was assessed using Firth’s penalized Cox regression, time-dependent AUC, and Brier scores. Results: Median follow-up was 73.3 months. In the overall cohort, NB offered stable discrimination over time compared to PS and RCB. However, performance differed notably by subtype. In luminal tumors, NB maintained consistent prognostic value, whereas the performance of RCB diminished, particularly in distinguishing low-risk patients from those with pCR (RCB-I vs pCR: HR 1.57, p=0.17). Conversely, in TNBC, RCB was exceptionally robust, with extensive residual disease (RCB-III) identifying a subgroup with an 11-fold increased risk of recurrence (HR 11.08, p<0.001). IDI analysis revealed that NB offered the greatest improvement in predictive performance over time for luminal tumors, while RCB and NB showed equivalent, high performance for TNBC. Conclusions: Our findings suggest that the utility of post-NAC staging systems is phenotype-dependent. Neo-Bioscore provides the most robust risk stratification for luminal tumors, whereas RCB is the superior predictor for triple-negative disease, most likely due to the linear impact of residual burden on survival in this subtype. Selection of the appropriate prognostic model based on immunophenotype is essential to optimize adjuvant strategies. Five and 10-year performance metrics by staging system. AUC Brier score System 5 Years 10 Years 5 Years 10 Years Clinical 0.612 0.653 0.164 0.223 NeoBioscore 0.712 0.630 0.148 0.225 Pathologic 0.704 0.641 0.147 0.219 RCB 0.659 0.628 0.159 0.229