Assessment of pathologic response and long-term outcome in locally advanced breast cancers after neoadjuvant chemotherapy: comparison of pathologic classification systems.

PURPOSE: Several pathologic classification systems have been developed to evaluate tumor response after neoadjuvant chemotherapy (NAC) for breast cancer. We aimed to compare pathologic classification systems and to investigate prognostic factors and risk stratification according to molecular subtype in relation to survival.
METHODS: We retrospectively evaluated pathologic response after NAC in 485 breast cancer patients by applying the National Surgical Adjuvant Breast and Bowel Project B18 trial (NSABP-B18), Miller and Payne system, Chevallier's classification, Sataloff's classification, residual cancer burden (RCB), residual disease in breast and nodes (RDBN), and clinical-pathologic stage + estrogen receptor status and grade staging system (CPS + EG).
RESULTS: All seven classification systems were significantly associated with overall survival (OS) and distant disease-free survival (DDFS). Regarding intrinsic subtypes, all systems were significantly associated with OS and DDFS for triple-negative tumors. Only RCB had prognostic significance for all four subtypes in relation to both OS and DDFS, and RDBN in DDFS only for all subtypes. In risk factor analyses, lymphovascular invasion (LVI), as well as other classic pathologic prognostic factors such as tumor size, lymph node status, and hormonal receptor status, was significantly associated with both OS and DDFS for the entire study group. Regarding subtypes, LVI was associated with DDFS for each subtype except Luminal B-like tumors.
CONCLUSIONS: Our results suggest that pathologic classification systems that evaluate residual tumors in both breast and lymph nodes after NAC show better association with clinical outcome. Furthermore, combining LVI with other classic prognostic factors might have prognostic value for the assessment of treatment response after NAC.