Causes and Risk Factors of Male Breast Cancer

While breast cancer most often affects women (people assigned female at birth), about 1% of cases are diagnosed in men (people assigned male at birth). Male breast cancer arises as cells that develop into cancer change, divide, and spread within ducts and lobules—the same tissues affected in female breasts, which men have in smaller amounts. This results in the development of benign (noncancerous) or malignant (cancerous) tumors.

Primarily, male breast cancer is caused by elevated levels of the hormones estrogen and progesterone. However, this condition has a strong genetic component and can have other causes, such as liver disease, alcohol consumption, and estrogen treatments for prostate cancer, among others.

This article discusses the causes and risk factors of breast cancer in men.

Common Causes

Generally, cancers arise when healthy cells become abnormal, start to divide, and spread, and eventually lead to the formation of tumors. Male breast cancer, as with other cancers, arises due to mutations of the genes that work to repair damaged parts of cellular DNA.

There is no single cause of male breast cancer, but rather it is due to a combination of genetic and environmental factors. Cases have been linked with abnormally high levels of estrogen and progesterone, hormones primarily associated with the female reproductive system, that men have in smaller amounts. Below are common causes of male breast cancer.

Klinefelter's Syndrome

Klinefelter's syndrome, a rare congenital disease (disease present at or before birth) affecting about 1 in 1,000 men, is a common risk factor for breast cancer. Typically, male babies are born with an X and a Y chromosome, whereas females have two Xs. Breast cancer is more prevalent in men who have two or more X chromosomes as well as the Y chromosome.

This chromosomal disease causes a range of physical and mental developmental issues. Most with Klinefelter's syndrome are unable to produce children, and they develop smaller than normal testicles due to insufficient production of testosterone (a predominantly male hormone). This causes hormone imbalances that can lead to male breast cancer.

Genetic Mutation

Changes in the structure and activity of genes, most often BRCA1 and BRCA2, are closely linked to cancer formation. These genes are associated with the suppression of tumor growth, so when they mutate (change), male breast cancer can result.  

Radiation Therapy

Radiation therapy, a cancer treatment, can also lead to gene structure alterations leading to cancer development. A history of such treatment significantly increases the chances of developing breast cancer.

Hormone Treatments

Hormone imbalance is another significant risk factor. Medications that boost estrogen levels are sometimes used to treat prostate cancer but can significantly raise male breast cancer risk.

Testicular Conditions

Conditions impacting the testicles—such as undescended testicles or inflammation (orchitis)—or the aftereffects of surgery to remove them (orchiectomy), raise the risk of developing male breast cancer. As with hormone treatments, these conditions and treatments affect testosterone levels in the body, a significant factor in cancer formation.  

Other Kinds of Cancer

In some cases, cancers in other parts of the body spread to the breast. The malignant (cancerous) cells break off from tumors and move through the body either through the bloodstream or lymph vessels. This is called metastasis.

Other Health Conditions

Scarring and damage to the liver, or liver cirrhosis, can also affect hormone levels in men, leading to a higher risk of developing breast cancer. Having excess weight (a body mass index, or BMI, of 25 to 29) or obesity (BMI of 30 or higher) significantly increases the chance of men (especially older men) developing this condition.

Environmental Factors

Environmental factors, such as exposure to carcinogens (substances that can cause cancer) or chemicals, may also cause mutations or affect hormone levels. These can be risk factors for male breast cancer; however, research indicates this link is not as robust as other causes.

Genetics

The genetic mutations that cause male breast cancer are usually inherited and passed from parent to child. Therefore, a family history of the condition is a significant risk factor, accounting for nearly 1 in 5 cases.

Irregularities of the breast cancer gene, BRCA2, are the most consistent and common genetic link found. According to a 2022 study, those with a BRCA2 mutation are 80 times more likely to develop breast cancer. These mutations are congenital, and they run in families.

Mutations of several other tumor-suppressing genes have also been associated with breast cancer. These include:

• BRCA1
• Androgen receptor (AR)
• Checkpoint kinase 2 (CHEK2)
• CYP17A1 cytochrome P450
• Phosphate and tensin homolog (PTEN)

Lifestyle Risk Factors

Certain habits and lifestyle factors raise the risk of developing cancer. This doesn’t necessarily mean they cause the condition, but rather, they increase the chances that you'll develop it. Specific risk factors vary based on the type of cancer, but several associated with male breast cancer include:

• Alcohol: Alcohol consumption raises the risk of developing many types of cancer. Heavy and regular drinking can damage the liver, leading to cirrhosis and affecting hormone levels, which increases breast cancer risk.
• Insufficient exercise: Since obesity and excess weight raise the chances of developing breast cancer, a sedentary lifestyle increases cancer risk. Keeping up with a regular fitness routine can help prevent the condition.
• Diet: As with exercise, a poor diet can also cause weight gain and lead to obesity and overweight. Regulating what you eat can help keep male breast cancer at bay.  

Non-Modifiable Risk Factors

Like other cancers, some risk factors can’t be controlled with lifestyle changes. For male breast cancer, the primary non-modifiable risk factors are: 

• Age: Older people are at a higher risk of developing breast cancer. Researchers have found that most cases of male breast cancer are in men over age 60.
• Family history: Due to the genetic component of this disease, family history can be a significant risk factor. About 20% of those affected have a first-degree relative, such as a parent, sibling, or child, with breast cancer.
• Race: Racial status may affect your chances of developing male breast cancer as well as the outcomes of treatment. Black men are 70 times less likely to develop breast cancer than Black women, while White men are 100 times less likely to develop it than White women.

Summary

Though cases are much rarer in this population, men can also develop breast cancer. Generally, male breast cancer arises due to hormonal imbalances and genetic abnormalities, which may result from various diseases and conditions.

Klinefelter's syndrome, genetic mutations, hormone treatments, certain testicular conditions, and radiation therapy increase your chances of developing male breast cancer. In addition, obesity, older age, and a family history of the condition are significant risk factors.  

A Word From Verywell

If you believe you’re at risk for developing male breast cancer or suspect you have symptoms, speak with your healthcare provider about screening. Having a dialogue about your concerns with your healthcare provider, seeking treatment when necessary, and making positive lifestyle changes can be instrumental in managing this condition and promoting your overall well-being.