Male breast cancer is the same disease as breast cancer in women and is closely related to an increased exposure to the female hormone estrogen. Any injury or imbalance in the estrogen-testosterone ratio can increase a man’s risk of developing breast cancer. Other risk factors for this disease include:

• Family history (several female relatives diagnosed with breast cancer).
  
  
• Testing positive for mutations of the BRCA1 or BRCA2  genes. Mutations in these genes can significantly increase the chances of a man or woman developing breast cancer. Other gene mutations, including mutations of the CHEK2 gene, may play a role in the development of breast cancer in men.
  
  
• Klinefelter’s syndrome (a condition in which not enough testosterone is produced). This condition is present at birth (congenital) and occurs in about 1 out of 1,000 men.
  
  
• A history of mumps orchitis (testicular inflammation after the mumps).
  
  
• Undescended testicles (cryptorchidism).
  
  
• Testicular injury.
  
  
• Exposure to female hormones (e.g., through diet, medications, chemicals).
  
  
• Hormone therapy for prostate cancer.
  
  
• Cirrhosis of the liver.
  
  
• Cowden disease (a congenital condition involving multiple benign tumors).
  
  
• Radiation to the chest area. For those treated for Hodgkin’s lymphoma with radiation therapy to the chest before age 30, the chances of also developing breast cancer are higher than the general population.