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Aromatase inhibitors for breast cancer treatment
By Mayo Clinic staff
What are aromatase inhibitors?
Aromatase inhibitors are drugs that reduce the levels of estrogen in postmenopausal women. Three such drugs are anastrozole (Arimidex), letrozole (Femara) and exemestane (Aromasin). All three cause a marked reduction in your body's estrogen levels.
How do aromatase inhibitors work?
Aromatase inhibitors work by reducing the amount of estrogen your body makes. Your adrenal glands produce a substance called androstenedione, which gets converted into estrogen in tissues such as fat and muscle, as well as in breast cancers themselves. The conversion requires an enzyme called aromatase. Aromatase inhibitors stop the conversion of androstenedione to estrogen.
Unlike tamoxifen, aromatase inhibitors actually lower the amount of estrogen in your body. Tamoxifen, on the other hand, blocks estrogen's effects on tissues in your body, such as breast tissue. Aromatase inhibitors have the potential to work as well as tamoxifen, but with different side effects.
Who should take aromatase inhibitors?
Only postmenopausal women should take aromatase inhibitors. Aromatase inhibitor therapy may follow therapy with tamoxifen, or it may be used as adjuvant therapy after primary cancer treatment in women who can't take tamoxifen.
The American Society of Clinical Oncology (ASCO) recommends that adjuvant therapy for hormone receptor positive breast cancer in postmenopausal women include an aromatase inhibitor at some point — either initially or after a course of tamoxifen — to lower the risk of recurrence.
How long should you take aromatase inhibitors?
There's no clear guideline, as exists for tamoxifen, on how long to take an aromatase inhibitor. Current adjuvant therapy options include taking an aromatase inhibitor for five years after primary cancer treatment; taking tamoxifen for two to three years and then switching to an aromatase inhibitor for the next two to three years; or taking an aromatase inhibitor for five years after taking tamoxifen for five years.
What are the side effects and health risks of aromatase inhibitors?
Side effects of aromatase inhibitors are generally mild in most women. They include hot flashes, joint pain, muscle aches, headache and fatigue. The side effects — especially joint pain — can be quite prominent at times in some women.
Because they lower your estrogen levels, aromatase inhibitors could put you at greater risk of osteoporosis, which increases your chances of bone fractures. If you choose an aromatase inhibitor as adjuvant therapy, your doctor may monitor your bone mineral density while you're taking the medication. Lower estrogen levels also may lead to vaginal dryness and irritation.
Decreased estrogen levels also have an effect on your body's blood lipid levels. Some doctors are concerned that aromatase inhibitors might increase the risk of heart problems or cardiovascular disease. There's some evidence that the different aromatase inhibitors may have different effects on lipid levels. However, research is ongoing, and studies to date have provided conflicting results.
Aromatase inhibitors encompass a rapidly changing area of research, so ask your doctor about the latest information.
Side effects of hormone therapy for breast cancer Tamoxifen for breast cancer treatment
