Aromatase Inhibitors
Aromatase inhibitors lower the amount of estrogen in post-menopausal women who have hormone-receptor-positive breast cancer. The hormone estrogen delivers growth signals to the hormone receptors. With less estrogen in the body, the hormone receptors receive fewer growth signals, and cancer growth can be slowed down or stopped.
Before menopause, the ovaries produce most of a woman's estrogen, so reducing estrogen from other sources has little or no effect. But in post-menopausal women, most of the body's estrogen is made from another hormone, androgen. Aromatase inhibitors stop the enzyme called aromatase from turning androgen into estrogen, lowering the amount of estrogen produced OUTSIDE the ovaries. That means less estrogen in the bloodstream, less estrogen reaching estrogen receptors, and less cancer cell growth.
Clinical research on aromatase inhibitors
Clinical trials have shown the important benefits of aromatase inhibitors. Now medical experts consider aromatase inhibitors to be the new standard of care for post-menopausal women with invasive hormone-receptor-positive breast cancer, both early and advanced-stage.
The latest results of several major international trials showed that aromatase inhibitors work better than tamoxifen in post-menopausal women with early-stage breast cancer that is hormone-receptor-positive—estrogen-receptor-positive, progesterone-receptor-positive, or both.
Understanding aromatase inhibitors
Aromatase inhibitor medications include Arimidex (chemical name: anastrozole), Aromasin (chemical name: exemestane), and Femara (chemical name: letrozole). Each is taken by pill once a day, for up to five years. But for women with advanced (metastatic) disease, the medicine is continued as long as it is working well.
All three aromatase inhibitors work in similar ways, and are only given to post-menopausal women with hormone-receptor-positive disease. Your doctor will help you decide which of the three medicines is best for you based on the results of thorough testing. Clinical trials have tested these medicines in different ways.
The U.S. Food and Drug Administration (FDA) bases its approval of drugs on the results of clinical trials, many of which go on for years and test many patients. Each medicine is approved for certain types of use, or "indications."
The three aromatase inhibitors have some similar and some different indications for use:
- Arimidex is approved by the FDA for women with early-stage disease right after surgery.
- Aromasin is approved by the FDA for women with early-stage disease who have completed two to three years of tamoxifen.
- Femara is approved by the FDA for women with early-stage disease right after surgery. Femara is also approved by the FDA for women with early-stage disease who have completed five years of tamoxifen.
- All three aromatase inhibitors are also approved for women with advanced (metastatic) disease.
Are there any differences among the aromatase inhibitors?
If you're having side effects from one kind of aromatase inhibitor, your doctor might recommend that you try another kind with a different chemical make-up. Arimidex and Femara have a similar chemical structure. The make-up of Aromasin is different from that of Arimidex and Femara.
- Aromasin is a Type 1 "steroidal inhibitor," which stops the activity of the aromatase enzyme forever.
- Arimidex and Femara are both Type 2 "non-steroidal inhibitors." They also stop the activity of the aromatase enzyme, but not permanently.
The two types of aromatase inhibitors may have slightly different benefits and side effects. But no studies have yet directly compared one aromatase inhibitor to another. Also, the side effects for each of the medications might not be the same in each person. So it's possible that your doctor might switch you to a Type 1 if you weren't doing well on a Type 2.
Who can take the different aromatase inhibitors?
Aromatase inhibitors are not prescribed for women who are still having menstrual periods. If you were pre-menopausal when you were diagnosed, and you had chemotherapy and stopped getting periods by the end of treatment, then your doctor might consider an aromatase inhibitor—but only if you have really stopped having periods. Your period can still come back six months to a year or even two years after treatment.
To be sure that you're clearly in menopause, your doctor will probably wait six to 12 months after your last period before doing blood tests that can determine if you have really gone into menopause. While you're waiting to figure out your menopausal status, your doctor might put you on tamoxifen.
You and your doctor will only consider aromatase inhibitors if the potential benefits are likely to outweigh the side effects.
Getting the benefit from any medicine means that you have to take it as prescribed. For aromatase inhibitors, that means every day. And while you are on the medicine, it's important to see your doctor regularly to make sure the drug is working well for you, and to discuss other treatment options, if needed.
Keep reading to learn more about: