The role of postmastectomy radiotherapy in women with pathologic T3N0M0 breast cancer.

BACKGROUND: The authors determined the impact of postmastectomy radiotherapy (PMRT) on overall survival (OS) among patients with pT3N0M0 breast cancer in the National Cancer Data Base.

METHODS: A total of 3437 patients with pT3N0M0 breast cancer who initially were treated with mastectomy between 2003 and 2011 were identified. Of these women, 1644 (47.8%) received PMRT (67% treated with chest wall RT alone and 33% treated with chest wall and regional lymph node irradiation). Univariable and multivariable analyses were conducted to identify characteristics associated with PMRT and OS. In addition, propensity score matching and interaction effect testing also were performed.

RESULTS: PMRT was associated with age <40 years, private insurance coverage, treatment facility location within 10 miles of the patient's home zip code, Charlson-Deyo comorbidity score of 0, tumor size ≥7 cm, and treatment with chemotherapy or hormone therapy (all P<.05). PMRT was associated with improved 5-year OS (86.3% for patients treated with PMRT vs 66.4% for patients not treated with PMRT; P<.01). In addition to PMRT (hazard ratio, 0.72; 95% confidence interval, 0.59-0.87 [P<.01]), age ≤50 years, treatment at an academic/research program, Charlson-Deyo comorbidity score of 0, tumor size <7 cm, chemotherapy receipt, and hormone therapy receipt were associated with improved OS on multivariable analyses (all P<.05). Interaction testing found that PMRT improved OS independent of age, facility type, Charlson-Deyo comorbidity score, tumor grade and size, surgical margin status, and receipt of chemotherapy or hormone therapy (all P>.1). Finally, propensity score matching analysis confirmed the impact of PMRT on OS (P = .02). It is interesting to note that regional lymph node irradiation did not improve OS versus chest wall RT alone (P = .09).

CONCLUSIONS: Among patients with pT3N0M0 breast cancer in the National Cancer Data Base, PMRT was found to be associated with improved OS regardless of surgical margin status, tumor size, and receipt of systemic therapy. Cancer 2017;123:2829-39. © 2017 American Cancer Society.