Male breast cancer (MBC) represents < 1% of breast cancer patients, and limited data exists regarding metastatic MBC. To better characterize this patient subset, we performed a population-based study examining prognostic factors among patients with stage IV MBC.

Patients with stage IV MBC diagnosed between 1988 and 2012 were selected from the Surveillance, Epidemiology, and End Results database. Prognostic factors for overall survival (OS) and cause-specific survival (CSS) were evaluated.

Overall, 394 patients had metastatic disease meeting inclusion criteria. The median follow-up was 21 months. The 5-year OS and CSS rates were 21.1% and 38.3%, respectively. Of those with known progesterone receptor (PR) status, 52% were PR-positive, which was associated with better OS (P < .001) and CSS (P = .003). Overall, 197 patients (50%) received surgery for the primary tumor, and 197 (50%) did not. Patients undergoing surgery had longer median CSS than those who did not (36 vs. 21 months; P < .001). Additional factors that correlated with prolonged OS and CSS were smaller tumor size (≤ 2 cm; P < .05) and younger age (≤ 65 years; P < .05). In multivariate analysis, smaller tumor size, PR-positivity, younger age, and resection of the primary tumor were associated with longer OS and CSS (P < .05).

Although stage IV MBC has poor OS and CSS, patients with PR-positive disease, younger age (≤ 65 years), tumor size ≤ 2 cm, or who undergo surgery of the primary tumor have better OS and CSS. This is the largest study of stage IV MBC to date, and these findings address some of the questions regarding this rare presentation of breast cancer.