Molecular subtypes predict the prognosis of male breast cancer: a retrospective cohort study

Male breast cancer is rare, and something different from female breast cancer. The characteristics of molecular subtype in male breast cancer is unclear and lack of large-sample study.

A retrospective study was conducted to investigate the characteristics and prognosis of patients with male breast cancer using the data recorded in the Surveillance, Epidemiology, and End Results (SEER) database from 2010-2014. A total of 1,597 cases were enrolled with median age of 66 years. The study endpoint was considered as patient death. The molecular subtype was defined by estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) status, hormone receptor (HR) positive was defined as ER positive with or without PR positive, including 1,373 cases of HR⁺/HER2^- tumor (86%), 182 cases of HR⁺/HER2⁺ tumor (11.4%), 13 cases of HR^-/HER2⁺ tumor (0.8%) and 29 cases with triple negative (TN) tumor (1.8%), respectively.

There were significant differences in distributions of age, race, grade, tumor size and American Joint Committee on Cancer (AJCC) stage between different molecular subtypes. Patients of different molecular subtypes differed significantly in 5 years overall survival and cause-specific survival (CSS). Five-year CSS (5y-CSS) rates of different molecular subtypes was 89.2% (HER2^-/HR⁺), 78.4% (HER2⁺/HR⁺), 72.6% (HER2⁺/HR^-) and 43.2% (TN), respectively. According to Cox regression, age ≥65 years [P=0.001, hazard ratio (HR) =2.136 (1.372, 3.324)], ER negative [P=0.02, HR =2.481 (1.159, 5.319)], PR negative [P=0.007, HR =2.294 (1.256, 4.184)], TN subtype [P<0.001, HR =10.676 (4.441, 25.665)], AJCC stage IV [P<0.001, HR =21.222 (10.377, 43.4)], tumor size >5 cm or T4 [P<0.001, HR =2.577 (0.978, 6.792)], Stage M1 [P=0.001, HR =4.519 (1.929, 10.587)] and Black race [P=0.002, HR =2.322 (1.442, 3.74)] were independent prognostic factors for poorer CSS.

Just like female, molecular subtypes also varied in male breast cancer. It could be a predictor for survival and improve the strategy making in clinical practice.