Breast cancer: Do we know the causes ?

Many risk factors can increase your chance of developing breast cancer, but it is not yet

known exactly how some of these risk factors cause cells to become cancerous.

Hormones seem to play a role in many cases of breast cancer, but just how this happens is not fully understood.

DNA is the chemical in each of our cells that makes up our genes—the instructions for how our cells function. We usually look like our parents because they are the source of our DNA. But DNA affects more than how we look.

Some genes contain instructions for controlling when our cells grow, divide, and die.

Genes that speed up cell division are called oncogenes. Others that slow down cell division, or cause cells to die at the right time, are called tumor suppressor genes. Certain changes (mutations) in DNA that “turn on” oncogenes or “turn off” tumor suppressor genes can cause normal breast cells to become cancerous.

Inherited gene mutations

Certain inherited DNA changes can increase the risk for developing cancer and are responsible for the cancers that run in some families. For example, the BRCA genes (BRCA1 and BRCA2) are tumor suppressor genes. Mutations in these genes can be inherited from parents. When they are mutated, they no longer suppress abnormal growth, and cancer is more likely to develop.

Women have already begun to benefit from advances in understanding the genetic basis of breast cancer. Genetic testing can identify some women who have inherited mutations in the BRCA1 or BRCA2 tumor suppressor genes (or less commonly in other genes such as PTEN or TP53). These women can then take steps to reduce their risk of developing breast cancers and to monitor changes in their breasts carefully to find cancer at an earlier, more treatable stage.

Acquired gene mutations

Most DNA mutations related to breast cancer occur in single breast cells during a woman's life rather than having been inherited. These acquired mutations of oncogenes and/or tumor suppressor genes may result from other factors, like radiation or cancer causing chemicals. But so far, the causes of most acquired mutations that could lead to breast cancer are still unknown. Most breast cancers have several acquired gene mutations.

Tests to spot acquired gene changes may help doctors more accurately predict the outlook for some women with breast cancer. For example, tests can identify women whose breast cancer cells have too many copies of the HER2 oncogene. These cancers tend to be more aggressive. At the same time, drugs have been developed that specifically target these cancers.

Can breast cancer be prevented?

There is no sure way to prevent breast cancer. But there are things all women can do that might reduce their risk and help increase the odds that if cancer does occur, it is found at an early, more treatable stage.

Lowering your risk

You can lower your risk of breast cancer by changing those risk factors that can be changed (see the post, "What are the risk factors for breast cancer?").

Body weight, physical activity, and diet have all been linked to breast cancer, so these might be areas where you can take action.

Both increased body weight and weight gain as an adult are linked with a higher risk of breast cancer after menopause.

Alcohol also increases risk of breast cancer. Even low levels of alcohol intake have been linked with an increase in risk.

Many studies have shown that moderate to vigorous physical activity is linked with lower breast cancer risk.

A diet that is rich in vegetables, fruit, poultry, fish, and low-fat dairy products has also been linked with a lower risk of breast cancer in some studies. But it is not clear if specific vegetables, fruits, or other foods can lower risk. Most studies have not found that lowering fat intake has much of an effect on breast cancer risk.

At this time, the best advice about diet and activity to possibly reduce the risk of breast cancer is to:

Get regular, intentional physical activity.
Reduce your lifetime weight gain by limiting your calories and getting regular physical activity.
Avoid or limit your alcohol intake.

Women who choose to breastfeed for at least several months may also get an added benefit of reducing their breast cancer risk.

Not using hormone therapy after menopause can help you avoid raising your risk.

It’s not clear at this time if environmental chemicals that have estrogen-like properties (like those found in some plastic bottles or certain cosmetics and personal care products) increase breast cancer risk. If there is an increased risk, it is likely to be very small. Still, women who are concerned may choose to avoid products that contain these substances when possible.

Finding breast cancer early

Other than lifestyle changes, the most important action a woman can take is to follow the American Cancer Society's guidelines for early detection.
Early detection will not prevent breast cancer, but it can help find it when the likelihood of successful treatment is greatest.

For women who are or may be at increased risk

If you are a woman at increased risk for breast cancer (for example, because you have a strong family history of breast cancer, a known genetic mutation of a BRCA gene, or you have had DCIS, LCIS, or biopsies that have shown pre-cancerous changes), there may be some things you can do to reduce your chances of developing breast cancer. Before deciding which, if any, of these may be right for you, talk with your doctor to understand your risk and how much any of these approaches might lower this risk.

Genetic testing for BRCA gene mutations

Many women may have relatives with breast cancer, but in most cases this is not the result of BRCA gene mutations. Genetic testing for these mutations can be expensive and

the results are often not clear cut. Testing can have a wide range of consequences that need to be considered. It should only be done when there is a reasonable suspicion that a mutation may be present.

The U.S. Preventive Services Task Force (USPSTF) recommends that only women with a strong family history be evaluated for genetic testing for BRCA mutations. This group represents only about 2% of adult women in the United States.

The USPSTF recommends that women who are not of Ashkenazi (Eastern European) Jewish heritage should be referred for genetic evaluation if they have any of the following:

2 first-degree relatives (mother, sisters, daughters) with breast cancer, one of whom was diagnosed when they were younger than 50
3 or more first- or second-degree relatives (includes grandmothers, aunts) diagnosed with breast cancer