Causes and Risk Factors of Breast Cancer

woman in bra with breast cancer ribbon
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Breast cancer is influenced by heredity, but it can develop even if you don't have a family history or carry genes for the disease. There are a number of conditions and environmental exposures associated with alterations in the breast tissue that lead to breast cancer, including smoking, hormone therapy, having dense breasts, and being overweight.

Breast cancer affects one in every eight women throughout their lifetimes. While it is rare, men can develop breast cancer as well. Whether you have a family history of breast cancer or not, attention to the causative factors may help prevent you from developing the disease.

Common Risk Factors

Breast cancer occurs when there are slight changes in the cells and tissues of the breast. These altered cells cause the formation of a tumor (or more than one tumor). These tumors can be aggressive, invading normal breast tissue, and potentially even spreading to other parts of the body (including the bones, lungs, and brain) through the lymph nodes and bloodstream.

While the cause or causes of these cellular changes is not known, there are a number of factors associated with breast cancer. These risk factors increase the chance of developing the disease, and they may do so by causing the condition or by reducing the body's protection against it.

Age

It is estimated that 80 percent of women diagnosed with breast cancer are 50 or older. Most types of cancer, including breast cancer, occur more frequently with advancing age. This is due to the build-up of risk factors, age-related changes in the cells of the body, and declining immune system protection from cancer.

Age of First Menses and Menopause

Having your first menstrual period at an earlier age and experiencing menopause at a later age—meaning more years of having your period—is associated with a higher chance of developing breast cancer. This is believed to be due to the hormonal changes that occur each month with a woman's menstrual cycle.

Dense Breasts

You can't control whether you have dense breasts or not, and this characteristic is linked with an increased chance of developing breast cancer. Some efforts are underway to standardize mammogram reports of dense breasts and their associated breast cancer risks.

Hormone Therapy

Oral contraceptives and hormone replacement therapy contain estrogen and progesterone. These hormones have been linked with breast cancer, but they do not necessarily pose this risk for all women.

Your medical history and family history play a role in whether any type of hormone could increase your risk of developing breast cancer.

Previous Cancer

Women (and men) who have previously been diagnosed and treated for any type of cancer, especially breast or ovarian cancer, are at a greater risk of developing breast cancer.

Pregnancy and Breastfeeding

Women who never become pregnant or who have children at a later age are more likely to develop breast cancer. Breastfeeding is also associated with a lower risk of the disease. These factors are believed to be related to the protective effects of hormonal changes that occur during pregnancy and lactation.

Heredity and Genetics

Having a mother, sister, or daughter with breast cancer doubles your chances of getting the disease yourself. About 20 percent to 30 percent of women with breast cancer have a family history of the condition.

That said, hereditary breast cancer is complicated. Many breast cancer genes have been identified, but not all women with breast cancer have these genes, even when breast cancer runs in the family. And many women who have the genes do not have a family history of breast cancer.

Breast Cancer Genes

The most common genetic mutation is that of the BRCA gene pair, referred to as BRCA1 and BRCA2, but there are a number of breast cancer genes, which are often referred to as non-BRCA breast cancer genes. There are also probably additional breast cancer genes that have not yet been identified.

Because there are so many breast cancer genes, they are unlikely to cause breast cancer in the same way.

Having a breast cancer gene could predispose you to the condition. When a genetic predisposition is combined with other risk factors, it becomes even more likely that you will develop the disease.

If you have breast cancer in your family, your doctor might recommend that you have genetic testing.

Lifestyle Risk Factors

There are a few activities and exposures that are linked with breast cancer. While they are often described as lifestyle choices, some of these behaviors are in fact addictive, making them difficult to stop. If you drink, smoke, or consume an unhealthy diet, consider getting professional help if you want to change your habits.

Lifestyle risk factors associated with breast cancer include:

  • Smoking: Cigarettes contain a number of chemicals, many of which are known carcinogens. Smoking is associated with breast cancer, as well as a number of other types of cancer.
  • Alcohol consumption: Women who drink two to five drinks a day have 1.5 times the risk of getting breast cancer compared to women who do not drink alcohol.
  • Weight: Obesity may increase the risk of breast cancer. This is largely due to altered estrogen hormone levels that are associated with weight gain in women.
  • Diet: There have been a number of theories about food and breast cancer. Experts suggest that some food preservatives and dyes may be carcinogenic and can increase the risk of all cancers, including breast cancer.

About Soy

There have been many controversies regarding soy and breast cancer. Soy, which is present in a small number of foods—including meat substitutes, tofu, edamame, and miso—has been considered both a cause and a preventative strategy of breast cancer.

Experts still aren't in agreement about the impact of soy on breast cancer, so it is best to check with your doctor, especially if you have had breast cancer or are at risk of the disease.

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