Epidemiology of male breast cancer

Background: Male breast cancer is relatively rare (less than 1% of all cases of breast cancer) and usually treated similarly to female breast cancer. There are a very limited number of studies for characterization of male breast cancer, and most studies are small and underpowered. We report the results of a retrospective study using national cancer database from years 2004 to 2014. Purpose: The purpose of this study was to determine the survival and risk factors for male breast cancer in using a large study population in the United States. Methods: In this retrospective study we included 19,795 patients with a follow-up period of up to 11 years. In this population, the majority of patients were non-Hispanic white (74.8%), 12.1% were black, 0.5% were Hispanic, and the remaining were other races. Results: The rate of incidence was 7.2% in 2004 and increased to 10.3% in 2014. The significant predictors of mortality included cancer stage II, III, and IV vs stage 0 (hazard ratio [HR]: 1.5, 2.7, and 9.9, respectively), age (HR: 1.04), surgery (HR: 0.4), radiation (HR: 0.8), chemotherapy (HR: 0.8), hormonal (HR: 0.8), tumor size for every 10-mm increase (HR: 1.01), and estrogen receptor (ER)-positive and progesterone receptor (PR)-positive (HR: 0.8). Socioeconomic factors such as income, insurance, and facility type also contributed to the higher risk for mortality. Higher CharlsonDayo index resulted in higher mortality rate. Kaplan-Meier survival probability was higher in patients who underwent surgery (P\u3c0.001), received radiation (P\u3c0.001), received chemotherapy (P\u3c0.001), or received hormonal therapy (P=0.0126). The patients identified with ER and PR positivity (P\u3c0.0001) also had higher survival probability. In a subset of patients (n=7880), HER2/neu was available from 2010 to 2014). Survival probability was higher in patients with negative HER2/neu expression (P\u3c0.001), whereas mortality risk was 1.7 times higher among patients diagnosed with positive HER2/neu expression. Conclusion: This study with a large patient population showed that socioeconomic factors, cancer stage, tumor characteristics (size and grade), and higher Charlson-Dayo scores contributed to higher mortality among male patients diagnosed with breast cancer. Among treatment modalities, surgery was most effective followed by radiation, chemo-, and hormonal therapy. Patients identified with positive ER and PR had better survival probability. Biomarker identification followed by timely diagnosis of the treatment, irrespective of socioeconomic status, is likely to reduce the risk for mortality. A subset analysis showed that positive HER2/neu expression had higher mortality