Many patients with breast cancer respond to hormone therapy, a treatment strategy designed to inihibit proliferative signalling to cancer cells. Many breast cancer cells express a protein called the estrogen receptor, which sits on the surface of the cell and detects levels of circulating estrogen. When estrogen is present, the estrogen receptor becomes active, and tells the cancer cell to proliferate. Hormone therapies for the treatment of breast cancer can prevent the formation of estrogen to lower circulating estrogen levels, or prevent the estrogen receptor from sensing estrogen in the blood. Since estrogen signals to tissues other than breast tumors, the use of breast cancer hormone therapy has potential side effects.
Menopause-like Symptoms
The estrogen-blocking nature of hormone therapies leads to a menopause-like condition. Normally in menopause, the ovaries stop producing estrogen, which leads to a number of unpleasant side effects in many women as their body responds to the hormonal change. Use of hormone therapy for breast cancer mimics menopause, since the therapy prevents cells from responding to estrogen, so the cells act as if estrogen is not there.
MacMillan Cancer Support states that common menopause-like symptoms experienced in women receiving breast cancer hormone therapy are night sweats, chills, mood swings, difficulty concentrating, and a lower sex drive. Women experience severe side effects from hormone therapy should discuss their concerns with a physician.
Blood Clots
Another possible side effects for women taking hormonal therapy for breast cancer is the development of blood clots. Blood clots commonly occur in the lower extremities, and regions where the blood moves more slowly, and is therefore more prone to clotting, according to the Cancer Prevention Institute of California. Once formed, a blood clot can travel though the bloodstream into the heart or the lungs, where it can be fatal.
Many estrogen hormone therapies, including birth control pills, have a possible side effect of blood clotting. Women are more at risk of developing clots as they age, or if they have existing cardiovascular conditions.
Uterine Cancer
A rare side effect of hormonal treatment for breast cancer is the development of uterine cancer. This is a problem with a class of drugs called selective estrogen receptor modulators, or SERMs. SERMs are hormonal therapy treatments that bind to the estrogen receptor, preventing the binding of estrogen to the receptor on breast cancer cells, and therefore treating breast cancer. Many SERMs do not function the same way in uterine cells, which also produce the estrogen receptor protein.
According to the National Cancer Institute, some SERMs have the ability to bind to the estrogen receptor on uterine cells, and actually activate the receptor, signalling for proliferation of uterine cells. Over the course of hormone therapy, the uterus is constantly exposed to proliferative signals, which promotes the growth of tumors. Women with a family history of uterine cancer should discuss their concerns about hormonal therapy with their doctor.
