Abstract
BACKGROUND/AIM: Tumor microenvironment (TME) assessment is considered to play an important role in the prediction of prognosis and therapeutic response following breast cancer treatment. No consensus has been reached regarding evaluation methods despite reports on the utilization of tumor-infiltrating lymphocytes (TILs) for immune TME (iTME) monitoring. Optimum timing of iTME assessment has not yet been established. PATIENTS AND METHODS: Two hundred thirty-nine patients were treated with neoadjuvant chemotherapy (NAC). During the period from diagnostic needle biopsy to NAC initiation for breast cancer, the optimal evaluation timing was examined using a receiver operating characteristic (ROC) curve analysis. RESULTS: A significant correlation between TILs and pathological complete response (pCR) was only observed in the short-term group (≤35 days) (p=0.033). Prognostic analysis revealed that in the short-term group, patients with high TIL levels had a significantly better survival prognosis relative to those with low TIL levels (>35 days) [disease-free survival (DFS): p=0.001, overall survival (OS): p=0.021]. TILs were identified as an independent factor affecting DFS in a multivariate analysis (p=0.008, hazard ratio=0.130). CONCLUSION: TIL assessment during NAC for breast cancer is a prognostic predictor only when performed at ≤35 days before NAC initiation.