Evaluating the Tumor Burden, Histological Changes, and Immune Landscape of Breast Cancer Post-neoadjuvant Chemotherapy: Insights From 50 Cases

Breast cancer is a heterogeneous disease with variable responses to neoadjuvant chemotherapy (NACT). Evaluating the histopathological and immune changes in post-NACT breast cancer specimens is crucial for understanding treatment response and guiding further management. This study aims to assess tumor burden using the Residual Cancer Burden (RCB) index, examine histological alterations, evaluate immune activity through tumor-infiltrating lymphocytes (TILs), and analyze proliferative capacity via Ki-67 expression in post-NACT breast cancer specimens. A cross-sectional study of 50 modified radical mastectomy (MRM) specimens post-NACT was conducted. The histopathological analysis included tumor regression changes, stromal and cellular alterations, and nodal involvement. Immune response was assessed by quantifying TILs, and proliferation was measured using the Ki-67 index. Statistical correlations were made between clinicopathological parameters, TILs, and Ki-67 expression. Residual disease was detected in 39 cases (78%), and 11 cases (22%) had no residual disease. Among the 39 cases with residual disease, the majority were classified as RCB II (22 cases, 56%), 16 cases (41%) were classified as RCB III, and one case (3%) was classified as RCB I. Common histological changes post-NACT included fibrosis in 31 cases (62%), necrosis in 19 cases (38%), and infiltration by foamy histiocytes in 16 cases (32%). Malignant epithelial cells more frequently exhibited foamy cytoplasm (16 cases (41%) vs. two cases (5%); p=0.0003), hyperchromatic nucleus (26 cases (67%) vs. six cases (15%); p=0.0001), and prominent nucleoli (26 cases (67%) vs. four cases (10%); p=0.0001) compared to benign cells. Among the 39 cases with residual disease, low TIL and high Ki-67 expression were observed in 20 cases (51%), while 12 cases (32%) showed high TIL and low Ki-67. Residual tumors with high TIL and high Ki-67 (four cases, 10%) and low TIL and low Ki-67 (three cases, 8%) were less common. A significant inverse relationship was found between TIL levels and Ki-67 expression (p=0.0002), as tumors with low TIL were more likely to have high Ki-67 expression (20 cases, 51%), whereas those with high TIL more frequently exhibited low Ki-67 expression (12 cases, 32%). Post-NACT evaluation of tumor burden, immune landscape, and proliferation provides valuable prognostic insights. Integrating RCB, TILs, and Ki-67 into routine pathological assessment may aid patient stratification and guide personalized treatment strategies. Further large-scale studies are needed to validate these findings and improve therapeutic decision-making in breast cancer management.