The effect of neoadjuvant chemotherapy on tumor-infiltrating lymphocytes in patients with breast cancer

Aim: This study investigated the effect of neoadjuvant chemotherapy (NAC) on stromal tumor-infiltrating lymphocytes (sTILs) and their treatment response. Materials & methods: One hundred fifteen patients with pre-NAC core biopsies and post-NAC surgical resection specimens were reviewed. Results: There was no significant change between pre- and post-treatment sTILs. Both pre- and post-NAC sTILs were significantly lower in patients with luminal A subtype. An increase in sTILs was observed in 21 (25.9%) patients after NAC, a decrease in 29 (35.8%) and no change in 31 (38.3%; p = 0.07). Pretreatment sTIL density was independent predictor of pathological complete response in multivariate analyses (odds ratio: 1.025, 95% CI: 1.003-1.047; p = 0.023). Conclusion: High sTIL density in core biopsies was independently related to pathological complete response. In addition, ER appears to be the most crucial factor determining the rate of sTIL. Plain language summary New studies have shown that the tumor microenvironment is critical in tumor behavior. Immune cells surrounding tumor cells are the main components of the tumor microenvironment. Our study aimed to investigate the change in immune cells before and after chemotherapy in breast cancer patients. Our study included 115 patients. All patients underwent chemotherapy before surgery to shrink the tumor. Tru-cut biopsy pieces and the breast tissue obtained after surgery were examined. The presence of estrogen or progesterone receptors on tumor cells decreased the number of immune cells surrounding the tumor cells. The number of immune cells did not decrease after chemotherapy. Another finding was that the greater the number of immune cells around the tumor, the more likely that the tumor would disappear after chemotherapy.