The exact cause of breast cancer is unknown. But certain things can increase a man’s chances of developing it. These are called risk factors.

What are risk factors?

The exact cause of breast cancer is unknown. But certain things can increase a man’s chances of developing it. These are called risk factors. Because breast cancer in men is rare, most men who have these risk factors will never develop breast cancer.


The risk of breast cancer in men increases with age. It is most common in men over 60 years old. Breast cancer in young men is very rare.

Klinefelter syndrome

This is a rare syndrome that only affects men. Normally, males are born with one X chromosome and one Y chromosome (XY), and females have two X chromosomes (XX).

Men with Klinefelter syndrome have one Y chromosome and two or more X chromosomes (XXY or XXXY).

Symptoms of Klinefelter syndrome may include:

  • being taller than average
  • having increased breast tissue (gynaecomastia)
  • having lower levels of testosterone
  • having smaller testicles
  • infertility.

Men with Klinefelter syndrome have a higher risk of breast cancer. For most men, the lifetime risk of developing breast cancer is less than 1 in 1000. For men with Klinefelter syndrome, the risk is closer to 1 in 25 (4%).

Family history of breast cancer

Men who have close relatives with breast cancer may have an increased risk of developing breast cancer. Close relatives, sometimes called your first-degree relatives, are parents, children, sisters and brothers.

About 1 in 5 men with breast cancer (20%) have a close relative who has also had breast cancer.

The increased risk may be due to inherited faulty genes. Our genes store the biological information we inherit from our parents.

The genes most commonly linked to an increased risk of breast cancer in families are BRCA1 and BRCA2. Men in families with the BRCA2 gene are more likely to develop breast cancer than men in families with the BRCA1 gene. It is thought that the BRCA2 gene may cause up to 1 in 10 breast cancers in men (10%).

The chance of there being a faulty gene in a family is higher when:

  • a number of family members have been diagnosed with breast cancer or related cancers, such as ovarian cancer.
  • the family members are closely related
  • the family members were diagnosed at a younger age
  • a man in your family has been diagnosed with breast cancer.

If you are worried about breast cancer in your family, talk to your GP or breast specialist. They can refer you to a family history clinic or a genetics clinic.

Men with breast cancer may be offered genetic testing, even if they do not have a family history of breast cancer.


Being exposed to radiation may increase a man’s risk of breast cancer. Men who have had radiotherapy to their chest at a young age, for example to treat lymphoma, may have an increased risk.

Oestrogen levels

Men may be at risk of developing breast cancer if they have higher levels of oestrogen than normal. This can be caused by long-term (chronic) damage to the liver, such as liver cirrhosis. Liver damage can also be caused by drinking a lot of alcohol over a long period of time.

Oestrogen levels can also be affected by being very overweight. Increased levels of oestrogen can affect the growth of breast cancer cells.

Testicular effects

Conditions that affect or damage the testicles may also increase the risk of breast cancer. These include:

  • having undescended testicles
  • having surgery to remove one or both testicles
  • having mumps as an adult.

Some occupations

Men who work in hot environments, such as blast furnaces, steel works and rolling mills, may have a slightly increased risk. This is probably related to heat damage to the testicles.

Some studies have also linked long-term exposure to petrol and exhaust fumes with breast cancer in men.


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