Regular Aerobic Exercise Linked to Less Estrogen-Sensitive Breast Tissue in Premenopausal High-Risk Women

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Women with close relatives who've been diagnosed with breast cancer have a higher risk of developing the disease.

If you've had one first-degree female relative (sister, mother, daughter) diagnosed with breast cancer, your risk is doubled. If two first-degree relatives have been diagnosed, your risk is 5 times higher than average.

If your brother or father have been diagnosed with breast cancer, your risk is higher, though researchers aren't sure how much higher.

In some cases, a strong family history of breast cancer is linked to having an abnormal gene associated with a high risk of breast cancer, such as the BRCA1 or BRCA2 gene. In other cases, an abnormal PALB2 or CHEK2 gene may play a role in developing breast cancer.

There are lifestyle choices you can make to lower your risk, such as maintaining a healthy weight, exercising regularly, not smoking, and avoiding alcohol.

There are also other risk-reducing options, including more frequent screening, taking preventive hormonal therapy medicine, and preventive (also called “prophylactic”) surgery to remove the healthy breasts and ovaries. Prophylactic breast surgery may be able to reduce a woman's risk of developing breast cancer by as much as 97%. The surgery removes nearly all of the breast tissue, so there are very few breast cells left behind that could develop into a cancer.

Women with an abnormal BRCA1 or BRCA2 gene may reduce their risk of breast cancer by about 50% by having prophylactic ovary removal (oophorectomy) before menopause. Removing the ovaries lowers the risk of breast cancer because the ovaries are the main source of estrogen in a premenopausal woman's body.

Although prophylactic ovary removal can significantly reduce the risk of developing ovarian cancer -- and also reduce the risk of breast cancer when done before menopause -- this surgery is a serious choice that can have a considerable impact on your life. The sudden loss of estrogen can cause a range of side effects, such as hot flashes, depression, difficulty sleeping, and lessened sex drive. Estrogen loss may affect bone and heart health. Ovary removal also takes away your ability to have children.

A small study suggests that regularly doing 5 hours of aerobic exercise per week may help lower the amount of estrogen-sensitive tissue in the breast in women at high risk for breast cancer.

The researchers suggested that women at high-risk for breast cancer who may want to delay preventive surgery might want to consider doing 30 to 60 minutes of aerobic activity per day, five days per week.

The study was published online on Oct. 28, 2015 by the journal Breast Cancer Research and Treatment. Read the abstract of “Dose-response effects of aerobic exercise on estrogen among women at high risk for breast cancer: a randomized controlled trial.”

"Women who discover that they are at an increased risk of breast cancer, perhaps from an inherited gene mutation, have no easy option for avoiding cancer. Double mastectomy is considered an effective method of prevention, but that's an incredibly difficult decision to make," said Kathryn H. Schmitz, Ph.D., M.P.H., F.A.C.S.M., professor of epidemiology, and member of the Abramson Cancer Center at Penn Medicine. Dr. Schmitz is also a member of the Breastcancer.org Professional Advisory Board and was the lead author of the study. "These new results show that for women in this high risk category, aerobic exercise has a striking ability to reduce the hormonally sensitive tissue in the breast that we worry about most for breast cancer."

The study included 139 premenopausal women ages 18-50 who were considered to be at high risk for breast cancer because of an abnormal gene or family history. The women were randomly split into two exercise groups:

  • the high-dose group exercised 300 minutes per week on a treadmill
  • the low-dose group exercised 150 minutes per week on a treadmill
  • a control group of other high risk women exercised for less than 75 minutes per week on a treadmill

The exercise program lasted for about 5 months.

The researchers took blood and urine samples from each woman, as well as did breast MRI imaging, before and after each of five menstrual cycles during the study.

Over the course of the study, the amount of estrogen-sensitive tissue in the women’s breasts, as measured by MRI, changed depending on how much they exercised:

  • women in the control group had a 20% increase
  • women in the low-dose group had a 8% decrease
  • women in the high-dose group had a 12% decrease

The researchers said this implies a drop of about 10% of estrogen-sensitive breast tissue per 100 minutes of exercise.

Estrogen seems to be a factor in the relationship between aerobic exercise and a lower risk of breast cancer. Earlier studies have suggested that even moderate exercise can lower estrogen levels in the body, and intense exercise -- similar to what a competitive female athlete does -- leads to sharp drops in estrogen levels, breast shrinkage, and irregular or skipped periods.

"This research shows one more potential benefit of exercise for women at high risk for breast cancer," said Sue Friedman, executive director of FORCE (Facing Our Risk of Cancer Empowered), which helped recruit women for the study. "We hope this will lead to further research on ways in which high risk women can reduce their breast cancer risk."

Dr. Schmitz and her colleagues are currently seeking funding for a similar study in premenopausal women at average risk for breast cancer.

"We understand that exercise isn't a panacea that will prevent cancer from occurring in women at high risk," said Dr. Schmitz. "However, we do believe that exercise could delay the diagnosis, and reduce the stage and grade and severity of the tumor when it is diagnosed.

“I often meet women who say 'I just found out I am BRCA positive -- will exercise help me until I make my decision about my surgery?' And for years I had to say 'I don't know,'" Dr. Schmitz continued. "Now I can say the research suggests it's possible."

If you’re busy with work, household chores, and family matters, finding time to exercise almost every day can be hard. Exercising also can be extremely difficult if you’re recovering from breast cancer treatment. Still, it’s worth your while to make time to move, especially if you’re at high risk for breast cancer.

It can help to break up your exercise into 20- or 30-minute sessions that add up to about 5 hours per week. Walking is a great way to start. Maybe you walk 30 minutes before going to work and 20 minutes on your lunch break. You can add a few more minutes by parking farther away from your building or taking mass transit. Or you can make plans to walk with a friend after work -- you’re more likely to stick with exercise if someone else is counting on you. Plus, you can socialize at the same time.

Along with a healthy diet and lifestyle choices, regular exercise is one of the best things women can do to keep the risk of a first-time breast cancer or recurrence as low as it can be. This study adds to other research suggesting that regular exercise reduces breast cancer risk. Regular exercise also helps keep your physical and mental health in top shape. No matter how old you are, it’s never too late or too soon to get moving.

Visit the Breastcancer.org Exercise section for tips on exercising safely and how to stick to an exercise routine.



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