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Some cancers are stimulated to grow in response to certain hormones.
Hormone therapy blocks the effects of these hormones, depriving cancer cells of
the fuel they need to grow. Hormone therapy usually involves taking
medications. Using specific drugs to block hormone production or interfere with
its effect can slow or stop cancer growth and can shrink tumors in some cases.
Another type of hormone therapy is to remove part or all of an organ that makes
the hormones. Hormone therapy is a common treatment for prostate cancer
and certain kinds of breast and ovarian cancers.
Hormone Therapy for Breast Cancer
Breast cancer can be hormone-receptor positive or hormone-receptor
negative. If it is positive, the breast cancer has receptors for the hormones estrogen
(ER+), progesterone (PR+), or both. Most breast cancers are hormone-receptor
positive. About 25 to 30% are hormone-receptor negative. Compared to
hormone-receptor negative ones, hormone-receptor positive tumors tend to grow
slowly. They are also more common in women who have gone through menopause.
The main types of hormone therapy for breast cancer include:
-
Aromatase
inhibitors lower estrogen levels by blocking aromatase. Aromatase is an
enzyme in fat that converts other hormones into estrogen. These drugs do not
prevent the ovaries from making estrogen. Because of this, they are only
effective in postmenopausal women with ER+ breast cancer. -
Estrogen-receptor
downregulators (ERDs) occupy the estrogen receptor on breast cells,
including cancer cells. This blocks estrogen from attaching to the receptor.
ERDs can also reduce the number of estrogen receptors and change their shape.
When a receptor doesn’t look the way it should, estrogen won’t be able to
attach as easily. -
Gonadatropin-releasing
hormone agonists (GnRHs) shut down estrogen production in the ovaries. This
means they are only effective in premenopausal women. Some literature uses the
term luteinizing hormone-releasing hormone (LHRH) instead of GnRH. -
Selective
estrogen-receptor response modulators (SERMs) also attach and occupy
estrogen receptors in the breast to block estrogen.
Sometimes, doctors recommend removing the ovaries
(oophorectomy) to stop estrogen production for hormone-receptor positive breast
cancer.
Hormone Therapy for Prostate Cancer
Male hormones—androgens—are necessary for prostate cancer to
grow. Hormone therapy for prostate cancer deprives it of the hormones it needs
to grow. This is also called androgen deprivation therapy and androgen
suppression therapy. Surgically removing the testicles will take away the
source of the androgen, testosterone. However, medicines can accomplish nearly
the same effect and have largely replaced surgery.
The main types of hormone therapy for prostate cancer
include:
-
Anti-androgens compete with
testosterone to occupy receptors on prostate cells, including prostate cancer
cells. This blocks testosterone’s effects on the cells. -
CYP17 inhibitors block an enzyme the
body uses to convert cholesterol into testosterone. This lowers testosterone
production in the testicles and other tissues, such as the prostate. -
Estrogens are female sex hormones. They
counteract the effects of male hormones. Other types of hormone therapy have
replaced the use of estrogens. Doctors may still suggest this therapy in some
cases. -
Gonadotropin-releasing
hormone (GnRH) agonists bind to
receptors on the pituitary gland. These synthetic drugs chemically resemble
natural GnRH. Initially, this causes the pituitary to increase signals to the
testicles to produce more testosterone. After 7 to 10 days, the continued
presence of the drug on the receptor will actually decrease testosterone
production to almost nothing. -
GnRH antagonists also attach to pituitary receptors. However, they do not mimic natural
GnRH. As a result, they do not cause an initial flare of testosterone
production. This makes them safer for men with advanced prostate cancer.
Hormone Therapy for Ovarian Cancer
There are three main types of ovarian cancers—epithelial
tumors, germ cell tumors, and stromal tumors. Epithelial tumors account for 90%
of ovarian cancers. Stromal tumors are rare. They typically occur in older
women and develop in cells that produce hormones. Stromal tumors are the primary
kind of ovarian cancer that can respond to hormone therapy. Doctors rarely use
hormone therapy to treat epithelial tumors.
The main types of hormone therapy for ovarian cancer
include:
-
Aromatase
inhibitors lower estrogen levels by blocking estrogen production in tissues
other than the ovaries. This means they are only effective in postmenopausal
women. -
Gonadotropin-releasing hormone (GnRH) agonists
shut down estrogen production in the ovaries. Like breast cancer, these drugs
are useful in premenopausal women. -
Tamoxifen
is a SERM that blocks estrogen. Its main use is for breast cancer, but doctors
use it to treat stromal tumors as well.
Hormone
therapy is usually part of an overall treatment plan that includes other treatments,
such as chemotherapy. Talk with your doctor about all your treatment options
and ask what to expect. There are side effects from taking hormone therapy. Ask
about these as well. Being informed will help you be better prepared for your
treatment.