Hormones and Cancer: What You Should Know

Hormones are constantly at work in the body, carrying messages through the bloodstream that regulate important functions from sleep and appetite to fertility and mood. Most of the time, they help keep the body in balance. But under certain conditions, these same signals can influence chronic conditions, including cancer. 

In some cases, hormones can help reduce cancer risk, while in others, elevated levels or prolonged exposure may increase risk by promoting cell division or fueling cancers that have already formed. June Hou, MD, gynecologic oncologist, and Natalie Berger, MD, breast oncologist, share how hormones influence cancer risk, the impacts of long-term exposure, and how hormone-based therapies work. 

How do hormones influence cancer?

Hormone-sensitive cancers (also called hormone-dependent cancers) are cancers that rely on hormones, specifically estrogen, progesterone, or testosterone, to grow and survive. These are often referred to as hormone receptor–positive cancers and most commonly include breast, prostate, endometrial, and some ovarian cancers. 

Cancers are classified as hormone receptor–positive or hormone receptor–negative based on whether the cancer cells have proteins called estrogen or progesterone receptors. When these receptors are present, hormones can bind to them and "fuel” the cancer to grow. 

About 80% of breast cancers are hormone receptor–positive, meaning they have receptors for estrogen, progesterone, or both. These cancers depend on hormones to grow, making them responsive to treatments that block or lower hormone levels. Endometrial (uterine) cancer has one of the clearest hormonal links. Estrogen stimulates growth of the uterine lining, while progesterone helps regulate and balance that growth. When estrogen levels are high without enough progesterone to counteract them, the lining can become too thick (a condition called endometrial hyperplasia) which can increase cancer risk over time. Some ovarian cancers are also influenced by hormones. Lifetime exposure to estrogen is thought to play a role in risk. Factors that reduce ovulation, such as pregnancy and breastfeeding, are linked to lower risk.  

Hormones can influence cancer risk in both directions. Some exposures increase risk, while others are protective. This duality becomes especially important when considering hormone-based medications. 

Birth control pills, for example, are associated with a small increase in breast and specific types of cervical cancer risk in certain groups, particularly among people with persistent human papillomavirus (HPV) infection. But they can also significantly reduce the risk of ovarian and endometrial cancers. For many people, the protective benefits outweigh the risks, especially since the risks drop significantly once you stop the pills. Those tradeoffs are highly individual and should be determined between you and your healthcare provider.

Hormone therapy cancer treatment

In hormone-sensitive cancers, hormone therapy is often used to block hormones from binding to cancer cells or to reduce the body’s production of those hormones. This can slow tumor growth, shrink tumors before surgery, and reduce the risk of recurrence.  

Because these treatments depend on someone’s unique tumor biology, patients are first tested to determine whether their cancer has hormone receptors. This ensures that therapy is tailored to the specific characteristics of the cancer.

What increases hormone-related cancer risk?

Hormone levels can become imbalanced for a range of reasons. When these imbalances persist over time, they can increase your risk of cancer. Factors such as early menstruation (before age 12), late menopause (after age 55), conditions like polycystic ovarian syndrome (PCOS), obesity, nulliparity (a woman who has not carried a pregnancy to viability), and long-term hormone exposure can all raise lifetime hormone levels. Researchers are also studying environmental exposures, such as endocrine-disrupting chemicals found in some plastics and household products that may affect hormone levels.  

Hormone replacement therapy (HRT), also called menopausal hormone therapy, is commonly used to relieve symptoms of menopause, including hot flashes, sleep disturbances, and bone loss. These therapies typically include estrogen alone or a combination of estrogen and progesterone, delivered through pills, patches, gels, or other forms. 

HRT can significantly improve quality of life, but it has also been linked to an increased risk of certain cancers-particularly breast and endometrial cancers. The level of risk depends on the type of hormones used, how long they are taken, and your own health history. When deciding whether to start HRT, it is important to speak with your doctor to understand your options.

Hormones and cancer: what’s the takeaway?

It’s a complex relationship between hormones and cancer. In some cases, certain hormones can decrease cancer risk, while they increase risk of other cancers. When deciding about any new medication that may have hormonal implications, it’s important to speak to your doctor to weigh these factors.