Hormones
All humans have both "male" (testosterone) and "female" (estrogen) hormones naturally circulating in their body. Males normally have much higher levels of testosterone and lower levels of estrogen, compared to females. However, these low amounts of estrogen can be increased, either through the use of certain medications (including steroids) or through other conditions that can lead to more estrogen being produced. When this happens, the breast tissue in males will grow. Because cells that are growing and dividing have a greater risk of becoming cancerous, higher levels of estrogen can be a risk factor for the development of breast cancer in males.
Inherited Genetic Mutations
Cancer forms as a result of a number of genetic mutations that changes the characteristics of cells, causing them to grow uncontrollably. Some of these genetic mutations can be inherited from the parents. One such genetic mutation, a mutation in the BRCA gene, is often linked to both male and female breast cancer. The BRCA gene is responsible for the repair of damaged DNA and for stopping cells with damaged DNA from dividing. Because DNA damage is a way for the other genetic mutations necessary for cancer formation (also known as "acquired" mutations), an inherited mutation in the BRCA gene greatly increases an individual's risk of developing breast cancer. According to the American Cancer Society, 10 percent of the cases of male breast cancer are linked to a mutation in the BRCA gene, and a male with a BRCA mutation has a five to 10 percent chance of developing breast cancer.
Acquired Mutations
All kinds of cancer, including breast cancer in males, occur as the result of acquired genetic mutations in the cancerous cells. It takes many different genetic mutations to cause a cell to become cancerous. These mutations may cause the cells to grow more quickly than usual and to not respond to chemical signals from other cells to stop growing, even to proteins that are involved in DNA repair (which makes other mutations more likely to happen). In the case of breast cancer that is able to spread (metastasize), mutations must also occur that let the cancerous cells escape the healthy breast tissue.
