Tumor subtypes and survival in male breast cancer

Abstract

Purpose: Male breast cancer is an uncommon disease, and population-based information regarding prognostic factors is limited. Most cases are hormone receptor (HR) positive; however, the association of tumor subtype with overall survival (OS) and breast cancer-specific survival (BCSS) is unclear.

Methods: Using SEER data, we identified men with invasive breast cancer between 2010 and 2017 with known HR and HER2 status. We examined tumor subtypes by patient characteristics and performed multivariate Cox proportional hazards analyses to determine the associations of each variable with OS and BCSS.

Results: We included 2389 men with a median follow-up of 43 months (IQR 19-68). Median age was 66 years. Tumor subtype distribution was 84.1% HR+/HER2-, 12.7% HR+/HER2+ , 0.8% HR-/HER2+, and 2.3% triple-negative (TN). In univariate analysis, OS at 5 years was 76.5% for HR+/HER2-, 65.1% for HR+/HER2+ , 84.2% for HR-/HER2+, and 48.1% for TN (p < 0.0001). Of all subtypes, TN had the worst BCSS (p < 0.0001). Stage, tumor subtype and race were significantly associated with OS and BCSS in multivariate analysis. Adjusted Cox hazard ratios for OS by tumor subtype with HR+/HER2- as reference were 1.55 for HR+/HER2+ (p = 0.001), 1.1 for HR-/HER2+ (p = 0.888), and 3.59 for TN (p < 0.001).

Conclusion: We observed significant differences in survival outcomes by tumor subtype. Poor outcomes among men with HER2+ and TN disease suggest possible under-treatment, aggressive tumor biology, and/or more advanced disease at presentation. Studies to better understand the inferior survival for men with these subtypes are warranted and will likely require international collaboration.

Keywords: HER2; Hormone receptor; Male breast cancer; Outcomes; Survival; Tumor subtype.