Most breast cancers in men are ductal carcinomas. Ductal means the cancer started in the milk pipes of the breast, called ducts. These cancers are usually invasive because they start inside the duct and then break through the wall of the duct, growing into the normal surrounding breast tissue.
Breast cancer in men is a rare disease, accounting for ∼1% of all breast cancer cases. Although the epidemiologic literature regarding female breast cancer is extensive, relatively little is known about the etiology of male breast cancer (MBC).