Postmastectomy radiation therapy following pathologic complete nodal response to neoadjuvant chemotherapy: A prelude to NSABP B-51?

Purpose: The utility of post-mastectomy radiotherapy (PMRT) in women with a nodal complete response (CRn) to neoadjuvant chemotherapy (NAC) is unknown. The NSABP B-51 trial is evaluating this question, but has not reported results thus far. Therefore, we sought to answer this question with the National Cancer Database. Methods: The National Cancer Database was queried for women with cT1-4N1-3M0 breast cancer who had undergone NAC and were ypN0 upon mastectomy. Statistics included multivariable logistic regres-sion, Kaplan-Meier overall survival (OS) analysis, Cox proportional hazards modeling, and construction of forest plots. Results: Of 14,690 women, 10,092 (69%) underwent adjuvant PMRT and 4598 (31%) did not. The median follow-up was 55.6 months. In all patients, the 10-year OS was 76.3% for PMRT and 78.6% without (p = 0.412). There were no notable effects of PMRT on OS based on age or the axillary management (num-ber of nodes removed). Specifically, in the NSABP B-51 population of cT1-3 cN1 patients, the 10-year OS was 82.6% for PMRT and 80.0% without (p = 0.250). PMRT benefitted women with increasing cT stage (i.e. cT3-4), increasing ypT stages (with the exception of ypT4 potentially owing to small sample sizes), and cN3 cases (p < 0.05 for all). Conclusions: In the absence of published results from NSABP B-51, this assessment of over 14,000 women from a contemporary US database revealed that PMRT may be most useful for a moderately-high risk group - women with more advanced primary and/or nodal disease at diagnosis, yet with tumor biology favorable enough that the disease does not progress or remain stable after NAC. The OS findings notwith-standing, this study cannot exclude potential differences between groups in recurrence-free survival, which is the primary endpoint of NSABP B-51, While the results of the NSABP B-51 will confirm optimal management for patients with limited nodal disease having a CRn following NAC, the present results sug-gest PMRT should remain the standard of care for more advanced disease than NSABP B-51 eligibility criteria. (c) 2021 Elsevier B.V. All rights reserved. Radiotherapy and Oncology 162 (2021) 52-59

Automated summary

The study examined the utility of post-mastectomy radiotherapy in women with advanced primary and/or nodal disease, showing potential benefits for this higher risk group. However, it could not exclude differences in recurrence-free survival between groups.