Natural Killer Cell Activity and Response to Neoadjuvant Treatment in Breast Cancer Patients.

No validated biomarkers are available to monitor neoadjuvant treatment effects for breast cancer. Natural killer cell activity (NKA) has shown prognostic potential in other cancers. This study examined the association between NKA and treatment response. Patients had blood samples collected at baseline, before each treatment, and pre- and postoperatively. Plasma IFNγ levels were measured by ELISA as a surrogate marker of NKA, with 250 pg/mL as the cutoff for normal versus low NKA. Study endpoints were residual cancer burden (RCB) class, overall survival (OS), and invasive disease-free survival (IDFS). Seventy-eight patients were included. The five-year IDFS was 88.1% (95% confidence interval (CI) 73.7-94.9%) for patients with normal NKA versus 71.5% (95% CI 40.6-88.2%) for patients with low NKA (p = 0.049) preoperatively. At the fifth treatment cycle, the median IFNγ was 11 pg/mL (interquartile range (IQR) 0.5-124 pg/mL) in patients receiving supportive prednisolone and 753 pg/mL (IQR 192-1580 pg/mL) in patients not receiving supportive prednisolone. At the sixth treatment cycle, the corresponding values were 7 pg/mL (IQR 0-15 pg/mL) and 806 pg/mL (IQR 180-1631 pg/mL) (p < 0.0001). In conclusion, NKA may have prognostic potential as a biomarker. This study is the first to demonstrate that prednisolone impairs NKA measurement in breast cancer patients.