Male breast cancer is a rare disease, and occurs when a group of cancer cells (a tumor) start in the cells of the breast. Less than 1% of all breast cancer cases occur in men, and a man’s chances of getting breast cancer are approximately 1 in 1,000. Symptoms of male breast cancer may include: a lump felt in the breast, nipple pain or discharge, an inverted nipple, sores on the nipples or the area surrounding it, and lumps felt under the arm (enlarged lymph nodes). Physical exams and imaging tests such as MRIs, ultrasounds, and X-rays, can be used to diagnose this condition. Sometimes a biopsy is also required, where a needle is used to take a small piece of the breast tissue to exam under a microscope. Treatment varies on a case-by-case basis, and depends on factors including: size and location of the breast tumor, the stage of the cancer, and the results of laboratory tests.