Postmastectomy radiation therapy in breast cancer patients with micrometastatic disease in sentinel node dissection: A cohort study and meta-analysis

Aim: The potential role of postmastectomy radiation therapy (PMRT) on prognosis in patients with T1-2 breast cancer and micrometastatic disease in sentinel lymph node dissection (SLND) has not yet been established. The aim of this study was to investigate the impact of PMRT on prognosis in patients with T1-2 breast cancer and micrometastatic in SLND. Method: A register- and population-based cohort was utilized by identifying eligible patients on the research database BcBase 3.0. Multivariate Cox regression models were applied for survival outcomes. In addition, a systematic literature review and meta-analysis including all relevant studies on this topic was performed. Results: In total, 956 patients fulfilling the inclusion criteria were found through the BcBaSe 3.0 with 237 (25.0 %) receiving PMRT and 719 (75.0 %) not receiving PMRT. No statistically significant differences between the two patient groups in terms of neither breast cancer-specific (adjusted Hazard Ratio (HR): 0.49; 95 % Confidence Interval (CI): 0.14 - 1.73) nor overall survival (adjusted HR: 0.63; 95 % CI: 0.29 - 1.35) was found. In the pooled analyses after literature review, PMRT did not result in better breast cancer-specific (5 studies; pooled HR: 1.06; 95 % CI: 0.88-1.27; I2 = 1 %; low certainty of evidence) or overall survival (6 studies; pooled HR: 1.01; 95 % CI: 0.91-1.13; I2 = 10 %; low certainty of evidence). Conclusion: PMRT does not seem to impact survival in patients with T1 or T2 breast cancer with micrometastatic disease in SLND. Considering the low level of evidence and the relatively short follow-up of included studies, caution in interpreting the results into clinical practice is suggested.