Prognostic Impact of Radiation Therapy in Pure Mucinous Breast Carcinoma.

PURPOSE: Pure Mucinous breast carcinoma (PMBC) is an invasive breast cancer with favorable prognosis. While pathology-specific guidelines exist for PMBC regarding adjuvant chemotherapy and endocrine therapy, no recommendations exist regarding locoregional treatment based on tumor histology. Prognostic impact of radiotherapy for patients with PMBC remains unclear. MATERIALS AND METHODS: The National Cancer Database was queried (2004-2017) for patients with pN0M0 PMBC who underwent lumpectomy. Chi-square testing compared categorical frequencies between patients who received radiotherapy versus those who did not. Propensity score matching created a 1:1 matched cohort of patients who received radiotherapy and patients who didn't. Kaplan-Meier analysis evaluated overall survival (OS). Cox proportional hazard analyses identified clinical and treatment factors prognostic for OS. RESULTS: 17,259 patients met selection criteria; 11,087 (74%) received radiotherapy while 3852 (26%) did not. After PSM, radiotherapy (HR 0.629; 95% CI 0.531-0.746), endocrine therapy (HR 0.676; 95% CI 0.567-0.805), black race (HR 0.703; 95% CI 0.498-0.991), and private insurance (HR 0.184; 95% CI 0.078-0.432) were favorable prognostic factors on multivariate Cox regression analysis while age ≥ 70 years (HR 2.668; 95% CI 1.903-3.740), tumor size > 20 mm (HR 1.964; 95% CI 1.613-2.391), and CDCC score > 0 (HR 1.770; 95% CI 1.474-2.126) were unfavorable prognostic factors. After PSM, 5-year OS was 86% for those who received radiotherapy and 81% for those who did not (P < .001). CONCLUSION: This is the largest study to date on PMBC and the prognostic impact of adjuvant radiotherapy. Radiotherapy is associated with a survival advantage, suggesting omission of radiotherapy is not warranted.