A risk factor is anything that affects your chance of getting a disease such as cancer. Different cancers have different risk factors. For example, exposing skin to strong sunlight is a risk factor for skin cancer. Smoking is a risk factor for cancers of the lung, mouth, larynx (voice box), bladder, kidney, and several other organs.

But risk factors don't tell us everything. Having a risk factor, or even several, does not mean that you will get the disease. Some men with one or more breast cancer risk factors never develop the disease, while most men with breast cancer have no apparent risk factors. Even when someone has a risk factor, there is no way to prove that it actually caused the cancer.

We don't yet completely understand the causes of breast cancer in men, but researchers have found several factors that may increase the risk of getting it. As with female breast cancer, many of these factors are related to sex hormone levels in the body.

Aging

Aging is an important risk factor for the development of breast cancer in men. Men with breast cancer average about 67 years old at the time of their diagnosis.

Family history of breast cancer

Breast cancer risk is increased if other members of the family ("blood relatives") have had breast cancer. About 1 out of 5 men with breast cancer have close male or female relatives with the disease.

Inherited gene mutations

A mutation (change) in the BRCA2 gene, which is responsible for some breast cancers in women, probably accounts for about 1 out of 10 breast cancers in men. BRCA1 mutations can also cause breast cancer in men, but they seem to be responsible for fewer cases than mutations in the BRCA2 gene. People with these mutations typically have a strong family history of breast cancer, which often appears at a younger age (under 60).

Other mutations that may be responsible for some breast cancers in men include those in genes called CHEK2 and PTEN. See the section, "Do we know what causes breast cancer in men?" for more information on inherited breast cancer genes.

Klinefelter syndrome

This is a congenital (present at birth) condition that affects about 1 of 1,000 men. Normally the cells in men's bodies have a single X chromosome along with a Y chromosome, while women's cells have two X chromosomes. Men with this condition have cells with more than one X chromosome (sometimes as many as 4). This causes their testicles to be smaller than usual and not produce functioning sperm cells, making them infertile. Compared with other men, they have lower levels of androgens (male hormones) and more estrogens (female hormones). For this reason, they often develop gynecomastia (benign male breast growth).

Some studies have found that men with Klinefelter syndrome are more likely to get breast cancer than men in the general population. But this is a hard area to study because these are both uncommon problems, and it is hard to collect enough cases to be sure. The risk seems to be increased, but overall it is still low because this is such an uncommon cancer, even for people with Klinefelter syndrome.

Radiation exposure

A man whose chest area has been exposed to radiation (usually for treatment of a cancer inside the chest, such as lymphoma) has an increased risk of developing breast cancer.

Alcohol

Heavy alcohol intake increases the risk of breast cancer in men. This may be because of its effects on the liver (see below).

Liver disease

The liver plays an important role in sex hormone metabolism by making binding proteins that carry the hormones in the blood. These binding proteins affect the hormones' activity. Men with severe liver disease such as cirrhosis have relatively low levels of androgens and higher estrogen levels. Therefore, they may have an increased risk of developing breast cancer.

Estrogen treatment

Estrogen-related drugs are sometimes used in hormonal therapy for men with prostate cancer. This treatment may slightly increase their breast cancer risk. However, this risk is small compared with the benefits of this treatment in slowing the growth of prostate cancer.

Men taking high doses of estrogens as part of a sex change procedure may also have a higher breast cancer risk.

Obesity

Recent studies have shown that women's breast cancer risk is increased by obesity (being extreme overweight) during adult life. Obesity is probably a risk factor for male breast cancer as well. The reason is that fat cells in the body convert male hormones (androgens) into female hormones (estrogens). This means that obese men have higher levels of estrogens in their body. Some obese men may notice that they don't have to shave as frequently as other men. They might also have trouble fathering children. Regular exercise and maintaining a healthy weight may help reduce the risk of breast cancer, as well as that of many other diseases and cancers.

Conditions affecting the testicles

Some studies have suggested that certain conditions that affect the testicles, such as having an undescended testicle, having mumps as an adult, or having one or both testicles surgically removed (orchiectomy) may increase breast cancer risk. More research is needed in this area.

Certain occupations

Some reports have suggested an increased risk in men who work in hot environments such as steel mills. This could be because long-term exposure to higher temperature can affect the testicles, which in turn would affect hormone levels. Men heavily exposed to gasoline fumes may also have a higher risk. Further research is needed to confirm these findings.

Last Medical Review: 09/24/2008
Last Revised: 05/13/2009