Can internal mammary lymph nodes irradiation bring survival benefits for breast cancer patients? A systematic review and meta-analysis of 12,705 patients in 12 studies

Objective To evaluate the effect of prophylactic irradiation of internal mammary lymph nodes in breast cancer patients. Methods The computer searched PubMed, EMBASE, Web of science, CNKI, Wanfang Medical Network, the Chinese Biomedical Literature Database to find clinical studies on internal mammary lymph node irradiation (IMNI) in breast cancer. The quality of the included literature was evaluated according to the Newcastle–Ottawa scale. Stata14 software was used for meta-analysis. Results A total of 12,705 patients in 12 articles were included for meta-analyzed. Compared with patients who unirradiated internal mammary lymph nodes (non-IMNI), the risk of death for patients after IMNI was reduced by 11% (HR 0.89, 95% CI 0.79–1.00, P = 0.0470); DFS of group mixed N + patients (high risk group) was significantly improved after IMNI (HR 0.58, 95% CI 0.49–0.69, P < 0.001). Further subgroup analysis shows that compared with non-IMNI, DFS was significantly increased in N 1 or ypN 1 subgroup (HR 0.65, 95% CI 0.49–0.87, P = 0.003) and N 2 or ypN 2 subgroup (HR 0.51, 95% CI 0.37–0.70, P < 0.001) after IMNI, but there was no statistical difference in DFS between the IMNI and non-IMNI groups in N 0 subgroup (HR 1.02 95% CI 0.87–1.20, P = 0.794) and N 3 or ypN 3 subgroup (HR 0.85, 95% CI 0.49–1.45, P = 0.547). No serious incidents were reported in all the included studies, and most of the acute and late side effects were mild and tolerable. Conclusion Under modern radiotherapy techniques, IMNI can safely and effectively bring clinical benefits to N 1–2 breast cancer patients, but its role in N 0 , N 3 breast cancer patients remains to be further studied.