# Is There an Immune Effect of Exercise in Patients with Breast Cancer? A Systematic Review and Meta-Analysis

## TL;DR

This study reviews whether exercise affects the immune system in breast cancer patients, finding no significant changes in immune cell counts.

## Contribution

The study provides a systematic review and meta-analysis on the immune effects of exercise in breast cancer patients.

## Key findings

- Exercise did not significantly affect circulating natural killer cell counts or activity in breast cancer patients.
- No significant changes were observed in T-cell subpopulations or B-cell levels following exercise interventions.
- Exercise appears immunologically safe but may have effects beyond circulating immune cell counts.

## Abstract

Exercise is known to reduce the risk of developing breast cancer and improve survival in patients diagnosed with this disease. However, the biological mechanisms underlying these benefits are not fully understood. One possible explanation is that exercise may enhance the immune system’s ability to fight cancer cells. The immune system plays a crucial role in detecting and eliminating abnormal cells, but cancer cells can sometimes evade this defense. In this systematic review and meta-analysis, we examined all available scientific evidence on how exercise affects immune cells and immune-related markers in breast cancer patients. We also systematically analyzed this evidence to determine whether exercise can improve anti-tumor immunity. Understanding these immune effects may help explain why exercise benefits cancer patients and support the use of exercise programs alongside conventional therapies.

Background/Objectives: Physical exercise reduces breast cancer (BC) risk and improves survival, yet the biological mechanisms remain incompletely understood. Exercise may modulate systemic immunity and local immune cell infiltration in the tumor microenvironment. In this systematic review and meta-analysis, we examined the effects of exercise on immune cells and immune-related markers in patients with BC. Methods: This study followed PRISMA guidelines and was prospectively registered in PROSPERO (CRD420251082444). Four databases (PubMed, Web of Science, Scopus, and Cochrane Library) were searched from inception through December 2025. Randomized controlled trials evaluating exercise interventions in patients with BC or BC survivors and reporting immune cell outcomes were included. Meta-analyses were performed on studies reporting natural killer cells, natural killer cell activity, T-cell subpopulations, and B cells. Results: A total of 18 studies involving 911 participants (539 in exercise intervention groups) were included in the systematic review, with eight studies included in meta-analyses. Exercise interventions did not show significant effects on circulating natural killer cell counts, natural killer cell activity, T-cell subpopulations (CD3+, CD4+, and CD8+), or B-cell levels when compared to control groups. Conclusions: Exercise does not appear to induce consistent changes in resting circulating immune cell populations in patients with BC or BC survivors, indicating that exercise is immunologically safe while potentially exerting effects beyond circulating cell counts. Further large-scale research is required.