Postmastectomy radiation therapy for triple negative, node-negative breast cancer

Purpose: The use of post-mastectomy radiation therapy (PMRT) for patients with node-negative, triple negative breast cancer (TNBC) is controversial. This study of a large, contemporary US database described national practice patterns and addressed the impact of PMRT on survival for patients with node-negative TNBC. Methods: The National Cancer Data Base was queried (2004–2014) for women with non-metastatic TNBC with pT1-4N0M0 disease undergoing mastectomy. Use of PMRT was assessed. Multivariable logistic regression ascertained factors associated with PMRT use. The Kaplan–Meier analysis evaluated overall survival (OS) between patients managed with either PMRT or observation following mastectomy when stratifying by pT stage. Cox proportional hazards modeling determined variables associated with OS. Results: A total of 14,464 patients met the selection criteria; of these, 1,569 (10.8%) received PMRT, whereas 12,895 (89.2%) did not receive PMRT. Use of PMRT varied significantly with pT stage, with only 5.7% of T1 patients undergoing PMRT, while 51.6% of patients with T3 disease underwent PMRT. Use of PMRT was associated with superior OS for patients with pT3 disease but not for patients with other T stages. Greater age was associated with decreased likelihood of PMRT use, while increased T stage and positive surgical margins were associated with use of PMRT. On multivariate analysis, increased age, T stage, and positive surgical margins were associated with worse OS. Conclusions: In the largest study to date evaluating the use of PMRT in patients with node-negative TNBC, the use of PMRT was low in patients with T1 and T2 disease. Additionally, while an OS benefit was observed with the use of PMRT in patients with T3 disease, there was no benefit with the use of PMRT in other T stage groups. Further prospective studies are recommended to further elucidate the benefit on PMRT in patients with node-negative TNBC.