Abstract

Using real-world data from the National Cancer Database, we emulate the Selective Use of Postoperative Radiotherapy After Mastectomy (SUPREMO) phase III clinical trial to assess the impact of postmastectomy radiation therapy (PMRT) on overall survival (OS) among patients with intermediate-risk breast cancer. Among 49,335 patients who underwent mastectomy, 6882 (13.9%) received PMRT. There was no significant difference in OS between those who did and did not receive PMRT (HR: 0.98, 95% CI, 0.92-1.04). However, PMRT was associated with improved survival among the patient subgroup who had stage T3N0 breast cancer (HR: 0.72, 95% CI,
0.58-0.89).
Purpose: To emulate the Selective Use of Postoperative Radiotherapy After Mastectomy (SUPREMO) phase III clinical trial using real-world data to assess the impact of postmastectomy radiation therapy (PMRT) on overall survival (OS) among patients with intermediate-risk breast cancer. Patients and Methods: Using the National Cancer Database, women diagnosed between 2006 and 2013 with intermediate-risk breast cancer (defined as pT1-2N1; pT3N0; or pT2N0 and grade III or with lymphovascular invasion) and 0-3 positive axillary lymph nodes, who underwent total mastectomy, were identified as being in accordance with the SUPREMO trial protocol and included in this study. Multivariable logistic regression, Cox proportional hazards regression, and stabilized inverse probability of treatment weighting were used to explore the relationship between PMRT and OS. The effects of PMRT within subgroups were explored using multivariable interaction models.

Results: In total, 49335 patients were included in the study, with 6882 (13.9%) receiving PMRT. Patients with stage T3N0 cancer, 1-3 positive axillary lymph nodes, or positive surgical margins were more likely to receive PMRT. Overall, PMRT was associated with no significant improvement in OS (HR: 0.98, 95% CI, 0.92-1.04).
However, improved survival was observed among women with stage T3N0 cancer who received PMRT (HR: 0.72, 95% CI, 0.58-0.89).

Conclusion: Although PMRT may not be associated with improved OS among all intermediate-risk breast cancer patients with 0-3 positive axillary lymph nodes, the subgroup of patients with stage T3N0 cancer seemed to benefit from PMRT. The study’s retrospective nature introduces some uncertainty, but preliminary findings of the SUPREMO trial support these results.