International Journal of Science and Technology (IJST)

Role of Ki-67, Tumor-Infiltrating Lymphocytes (TILs-CD4 and CD8), and PD-L1 in Predicting pCR After Neoadjuvant Chemotherapy for Breast Cancer

Neoadjuvant chemotherapy (NACT) has become a standard treatment approach in breast cancer management, enabling in-vivo assessment of tumour chemosensitivity and facilitating breast-conserving surgery. Pathological complete response (pCR) serves as a validated surrogate endpoint for survival, particularly in aggressive subtypes. This review examines the predictive and prognostic roles of three key biomarkers—Ki-67, tumor-infiltrating lymphocytes (TILs including CD4+ and CD8+ subsets), and PD-L1—in forecasting pCR following NACT. Ki-67, a nuclear proliferation marker, consistently associates with treatment responsiveness, though its predictive value varies by breast cancer subtype and cut-off threshold. TILs, reflecting the immune landscape of the tumour microenvironment, demonstrate subtype-dependent predictive significance, with the strongest correlations observed in triple-negative (TNBC) and HER2-positive cancers. PD-L1, a mediator of immune evasion, emerges as a prognostic marker, particularly in residual disease. Individually and collectively, these biomarkers offer clinically actionable information for treatment stratification, potentially reducing unnecessary chemotherapy exposure and guiding immunotherapy candidacy. Standardised scoring protocols and molecular profiling advances will be essential to embed these biomarkers reliably into routine clinical practice. Keywords: Ki-67; Neoadjuvant chemotherapy; PD-L1; Pathological complete response (pCR); Predictive biomarkers; Tumor-infiltrating lymphocytes (TILs)