Background: The 21-gene recurrence score (RS) is a RT-PCR assay estimating risk of distant recurrence in estrogen receptor positive (ER+), human epidermal growth factor receptor 2 negative (HER2) breast cancer (BC). Studies validating RS are limited to women. Our objective was to assess RS distribution and factors associated with high-risk RS in male BC. Methods: Using the Surveillance, Epidemiology, and End Results database, we identified men and women with ER+/HER2− BC from 2010 to 2013. Patients were categorized into risk groups using the traditional and the Trial Assigning Individualized Options for Treatment (TAILORx) cutoffs. Multivariable logistic regression determined factors associated with testing and high-risk TAILORx RS. Results: We identified 1388 men and 154,196 women with ER+/HER2− BC. Twenty-five percent of men and 30% of women had RS testing. Mean age of tested men was 63; most were white (81%), had grade I or II tumors (67%), and had stage I or II (95%) BC. Factors associated with increased RS testing were younger age, recent year of diagnosis, lymph node negativity, and lower-stage tumors (p ≤ 0.05). By TAILORx, 21% of men had high-risk RS compared with 14% of tested women. Men with grade III and PR negative tumors were more likely to have a high-risk RS (p ≤ 0.05). Chemotherapy utilization was correlated with RS. Conclusions: Using a large population-based dataset, we found that compared with women, men were significantly more likely to have high-risk RS. Grade III and PR-negative BC were significantly associated with high-risk RS. Higher RS in men correlated with increased chemotherapy utilization.
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