Predictors of adjuvant radiation therapy in the treatment of male breast cancer and its impact on outcomes: A propensity matched analysis.

Abstract

e12516 Background: Male breast cancer (MBC) accounts for 1% of all breast cancers and there is a paucity of data on factors impacting the treatment strategies and outcomes. We hypothesized that adjuvant radiation therapy (Adj-RT) may improve survival outcomes and sought to examine predictive factors for Adj-RT receipt. Methods: We queried the National Cancer Database (NCDB) for patients with stages I-III MBC treated with surgery (breast conservation surgery- BCS or mastectomy-MS) within 180 days of diagnosis (years 2004-2015). Multivariable logistic regression identified predictors of adjuvant radiation therapy receipt. Multivariable Cox regression evaluated predictors of survival. Propensity matching for adj-RT accounted for indication biases. Results: We identified 6,217 patients meeting the eligibility criteria (1457 BCS vs. 4760 MS). The majority of patients were white (85%) and within the age range of 50-80 years (74%). Although Adj-RT was omitted for 30% of BCS patients, the utilization was higher compared to MS (OR=26, p-value=0.001). The predictors of Adj-RT use were – African American race, higher stage, higher grade, presence of lymphovascular invasion and ER/Her-2 positivity for the entire cohort and higher age, urban location and higher income for BCS. Adj-RT was associated with lower mortality in the propensity matched model (overall HR for BCS=0.28, p-value<0.001; overall HR for MS=0.62,p-value=0.001) and is shown in the table. Conclusions: This study demonstrates there may be an association between decreased mortality and Adj-RT in MBC undergoing BCS. Although this implies that Adj-RT should be routinely delivered, it appears to be omitted frequently and its use requires further investigation. The study also suggests a benefit to Adj-Rt after MS for stage-III MBC. [Table: see text]