A potential role for peripheral natural killer cell activity induced by preoperative chemotherapy in breast cancer patients

Tumor-infiltrating lymphocytes are an important prognostic factor after neoadjuvant chemotherapy (NAC) in patients with breast cancer. Natural killer (NK) cells play critical roles in antitumor immune surveillance. Here, we assessed the relationship between peripheral natural killer (pNK) cell activity, tumor microenvironmental factors (TMEFs), and the therapeutic efficacy of preoperative chemotherapy in patients with breast cancer. In a cohort of 39 patients diagnosed with stage II–IV breast cancer who received NAC, we measured pNK cell activity by chromium release assay and assessed TMEF levels by next-generation sequencing. Following NAC, pNK cell activity was increased in 24/39 patients but decreased in 15/39 patients. Increased pNK cell activity following preoperative chemotherapy was associated significantly with the disappearance of axillary lymph node metastasis (Ax+; p = 0.0235). Increased pNK cell activity remained significantly associated with the disappearance of Ax+ in multivariate logistic regression analysis (OR 5.41, 95% CI 1.19–24.52, p = 0.0283). A Grade 2 or higher effect of NAC was associated with high pre-NAC cytotoxic T lymphocyte-associated protein 4 (CTLA-4) levels (p = 0.0281) and elevated post-NAC NK (p = 0.0005) cells and transforming growth factor-beta (TGF-β; p = 0.0350) levels. The disappearance of Ax+ was associated with high pre-NAC CTLA-4 levels (p = 0.0278) and elevated CD4 levels after NAC (p = 0.0250). The systemic activation of pNK cells after NAC may improve metastatic tumor elimination in patients with breast cancer owing to a release from local immunosuppression, and immune activation in the tumor microenvironment.