Association of Postmastectomy Radiation Therapy with Overall Survival for Women with pT3N0 Breast Cancer: An NCDB Analysis

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International Journal of Radiation Oncology, Biology, Physics


Purpose/Objective(s): Patients with pT3N0 breast cancer following mastectomy and axillary staging constitute a heterogeneous population with outcomes dependent on underlying tumor biology and treatment received. We analyzed the NCDB to compare overall survival (OS) rates of patients with pT3N0 disease treated with mastectomy with or without postmastectomy radiation therapy (PMRT). Materials/Methods: Patients with pT3N0 breast cancer (2004-2014) were included in this NCDB retrospective cohort analysis. Patients receiving neoadjuvant chemotherapy were excluded. Propensity scores were generated using logistic regression. Inverse probability of treatment weighting (IPTW) was utilized to account for confounding variables. Univariate and subset analyses were performed using the IPTW-weighted Kaplan-Meier method. Multivariate modeling was performed using the Cox proportional hazards model, with a double robust model reported utilizing IPTW. Hazard ratios are reported with 95% confidence intervals. Results: We identified 4,285 patients with pT3N0 disease treated with mastectomy, of which 43% also received PMRT. Following IPTW, all baseline factors were similar. Univariate analysis revealed an OS advantage with PMRT compared to mastectomy alone (HR: 0.43 [0.37- 0.49], 5-year estimate - 82.0% vs. 74.8%, p Z 0.0002). Doubly robust weighted cox modeling demonstrated a persistent benefit of PMRT over mastectomy alone, with a HR of 0.804 (0.704-0.918). Subset IPTW analysis revealed a benefit of PMRT if patients received hormonal therapy (HR: 0.64 [0.51-0.79]), but the benefit was not statistically significant in those receiving chemotherapy (HR: 0.85 [0.67-1.1]). While patients with right-sided disease benefited from PMRT (HR: 0.74 [0.6-0.9]), those with left-sided disease did not show a benefit with PMRT (HR: 0.89 [0.74- 1.06]). Conclusion: We identified an overall survival benefit for PMRT among a recent cohort of patients with pT3N0 breast cancer; this benefit persisted on univariate, multivariate, and IPTW analyses. There may be subsets of patients with pT3N0 disease that receive a limited benefit from PMRT, including those who receive adjuvant chemotherapy. Longer follow-up and information regarding cause-specific mortality would help confirm the lack of benefit of PMRT in patients with left-sided disease. Potential differences in outcome may be due to radiation-induced cardiac toxicity in this cohort, an outcome that is not able to be assessed with the NCDB. Future studies are needed to properly identify who benefits most from PMRT to minimize treatment-related toxicity which may have a significant impact on overall survival.





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