Relationship between the change in tumour-infiltrating lymphocyte level and residual tumour after neoadjuvant chemotherapy in patients with locally advanced breast cancer.

To evaluate the tumour-infiltrating lymphocyte (TIL) rates in breast tissue before and after neoadjuvant chemotherapy (NAC) and their impact on survival, eighty-four patients with locally advanced breast cancer (LABC) were assessed. Pre- and post-NAC TIL levels were determined using biopsy and surgical specimens, respectively. The median TIL rate was significantly different before (17.5%) and after (5%) NAC. Pre- and postoperative Ki-67 index, molecular subtype, pre- and post-NAC TIL concentration, and preoperative residual-cancer-burden TIL were significantly associated with pathological complete response (pCR). Specifically, higher pre-NAC TIL levels were associated with higher pCR rates. Postoperative Ki-67 index and pCR, and postoperative Ki-67 index were significant predictors of disease-free (DFS) and overall survival, respectively. The independent prognostic factors for DFS were postoperative Ki-67 score (hazard ratio [HR]: 6.16;  = 0.012), post-NAC TIL score (HR: 0.42; P = 0.041), and pCR (HR: 0.10; P = 0.038). Our study confirms that higher pre-NAC and lower postoperative TIL levels may be surrogate factors for longer DFS, and postoperative TIL rate may predict post-NAC pCR in patients with LABC.