The use of adjuvant radiation therapy in male breast cancer and its impact on outcomes.

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 sought to use a large national database to examine trends and predictors of the use of adjuvant radiation (Adj-RT), as well as any association with outcome. 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 adj-RT receipt. Multivariable Cox regression evaluated predictors of survival. Propensity matching for adj-RT was used to account for indication biases. RESULTS We identified 6,217 patients meeting the eligibility criteria (1457 BCS vs. 4760 MS). The majority of patients were Caucasian (85%) and in an 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 included African-American race, more advanced stage, higher grade, presence of lymphovascular invasion, and ER/Her-2 positivity for the entire cohort and increased 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). CONCLUSION This study demonstrates that while adj-RT after BCS is associated with decreased mortality in MBC patients, adj-RT is omitted in up to a third of cases of MBC after BCS despite being standard of care.