Hormones and Breast Cancer Risk

Understanding how hormones work is crucial to lowering your cancer risk

Hormones are your body’s chemical messengers, influencing everything from your metabolism and mood to your reproductive cycle and bone health.

Though they’re essential, over time they also influence how certain cells behave — and sometimes become the engine that fuels certain types of cancers.

“Hormones like estrogen and progesterone are an essential part of normal biology, but prolonged exposure can influence how abnormal cells grow and divide,” says Rebecca Jordan, DO, a breast surgical oncologist at Geisinger. “And being exposed to high levels over a lifetime has been linked to an increased risk of breast, ovarian and endometrial cancers in women.”

This isn’t to say hormones are the enemy — far from it. But understanding how they work can help you make more informed decisions to protect your health and lower your risk of breast and ovarian cancer.

Hormones and breast cancer: What’s the connection?

Hormones like estrogen and progesterone don’t cause cancer, but they can encourage certain cancers to grow and multiply.

In healthy cells, these hormones attach to proteins (called hormone receptors) that signal cells to grow and divide. But in cancer cells, those same signals can accelerate abnormal growth.

Most breast cancers are hormone receptive positive (HR+) — meaning the cancer cells rely on estrogen and/or progesterone to grow. They include:

ER+ (estrogen receptor positive)
PR+ (progesterone receptor positive)
Triple positive breast cancer, a subtype where cancer cells are ER+, PR+ and HER2+ (human epidermal growth factor receptor 2)

“In these cancers, blocking estrogen and progesterone from reaching these receptors can slow or stop tumor growth,” says Dr. Jordan. “Depending on your pathology report, your oncologist can determine whether hormone-blocking treatment is right for you.”

Why lifetime exposure to hormones matters

Long-term exposure to estrogen and progesterone can increase your risk for breast and ovarian cancer.

Factors that increase your lifetime exposure include:

Starting your period before age 12
Going through menopause after age 55
Never having children or breastfeeding
Taking hormone replacement therapy for menopause symptoms
Higher body fat after menopause (since fat tissue at this stage produces estrogen)

“A longer reproductive lifespan increases the total exposure to estrogen and progesterone,” says Dr. Jordan. “So, factors that reduce ovulation, like pregnancy and breastfeeding, can offer some protection and reduce your risk for certain cancers.”

Does hormone therapy affect cancer risk?

Hormone replacement therapy has been used for many years to relieve symptoms of menopause and help prevent osteoporosis. But if you’re considering the treatment, be sure to weigh the benefits against potential risks.

While research is variable, studies have shown some forms of hormone replacement therapy, especially those that combine estrogen and progesterone, may raise your breast cancer risk when taken for more than 5 years during menopause.

Long-term postmenopausal hormone therapy may also slightly raise the risk of ovarian and endometrial cancers — particularly with estrogen-only regimens and use for more than 5 years.

“These findings highlight the need for personalized medical advice when considering hormone therapy,” says Dr. Jordan. “Always discuss your personal and family history with your doctor before starting any hormone treatment.”

Tips to reduce breast and ovarian cancer risk

While you can’t change your genes or reproductive history, you can take steps to improve your lifestyle habits and reduce your risk for breast and ovarian cancers:

Maintain a healthy weight, especially after menopause, and eat a balanced diet.
Stay physically active, aiming for at least 150 minutes of moderate activity each week.
Limit alcohol to no more than 1 drink a day for women.Quit smoking.
Breastfeed your baby.
Know your family history and discuss it with your doctor.
Weigh the benefits vs. risks of hormone replacement therapy with your doctor.

Besides making changes in your daily habits, regular screenings and early detection strategies remain crucial in the fight against breast and ovarian cancers.

Regular mammograms and clinical breast exams can help detect breast cancer in its early stages, when it’s most treatable. If you’re in your 20s or 30s, start getting a clinical breast exam every 1 to 3 years from your primary care provider or gynecologist. If you’re over 40, talk to your doctor about your risk factors — they’ll determine how often you should have a screening mammogram.

And while there’s no standard screening for ovarian cancer, knowing your risk factors, regular checkups and watching for signs are essential.

“Early detection is your best defense,” says Dr. Jordan. “By understanding your unique risk profile, you can work with your healthcare team to develop a personalized plan for early detection and risk reduction — and beat the odds if you’re diagnosed.”