Dynamic changes in peripheral B and NK cells reflect treatment response in breast cancer subtypes.

BACKGROUND: The immune microenvironment plays a critical role in breast cancer progression and therapeutic response. Among circulating immune cells, B cells and natural killer (NK) cells have shown distinct and potentially opposing roles in tumor dynamics. However, whether dynamic changes in peripheral blood B- and NK-cell percentages are associated with treatment response across molecular subtypes of breast cancer remains unclear. METHODS: Peripheral blood samples were collected from breast cancer patients before and after standardized subtype-guided therapy (chemotherapy, anti-HER2 therapy, and/or endocrine therapy according to clinical guidelines). Flow cytometry was performed to quantify the percentage of B cells and NK cells within CD45 + lymphocytes. Spearman's rank correlation was used to evaluate associations between B and NK cell percentages. Paired comparisons were performed using the Wilcoxon signed-rank test. Treatment efficacy was defined as objective response rate (complete response + partial response, CR + PR) according to RECIST criteria. Patients with decreased B cell percentage and increased NK cell percentage after treatment were defined as the B-NK group. RESULTS: Subtype A (-- group) exhibited significantly higher B cells percentages and lower NK cells percentages compared with other subtypes (P < 0.05). A significant negative correlation between B and NK cell percentages was observed in overall cohort and in most subtypes. In subtype A, B cell percentage significantly decreased after treatment (P < 0.05), whereas NK cell percentage showed variable changes. Patients classified into the B-NK group tended to have a higher objective response rate compared with non-B-NK patients across subtypes. CONCLUSIONS: Peripheral blood B and NK cell percentages exhibit dynamic and partially coordinated changes during treatment. A pattern characterized by decreased B cell percentage and increased NK cell percentage may be associated with treatment response. These findings are exploratory and hypothesis-generating, and further validation in prospective, well characterized cohorts is required before potential clinical application.