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  • Side Effects of Aromatase Inhibitors


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    Breast Cancer 101 (Interactive Multimedia) - Aromatase Inhibitors
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    If you have hormone receptor-positive breast cancer, hormone therapy with tamoxifen and/or an aromatase inhibitor (anastrozole, letrozole or exemestane) is a key part of your treatment.

    Aromatase inhibitors are only used to treat postmenopausal women. Premenopausal women should not take aromatase inhibitors. And, women with certain heart problems should not take the aromatase inhibitor anastrozole.

    Compared to chemotherapy, aromatase inhibitors have few side effects. For example, they do not cause nausea.

    Joint and muscle pain

    Joint pain (arthralgia – ar-THRAL-juh) and muscle pain (myalgia – my-AL-juh) are common side effects of aromatase inhibitors [73-74]. The pain may be in the hands and wrists, feet and ankles, knees, back or other parts of the body.

    Up to 36 percent of women in clinical trials of aromatase inhibitors have reported joint pain and up to 15 percent have reported muscle pain (other studies have found even higher rates of these side effects) [73-75]. These symptoms can mimic carpal tunnel syndrome (in rare cases, aromatase inhibitors can cause carpal tunnel syndrome).

    Although aromatase inhibitors can cause joint and muscle pain, they do not cause permanent joint or muscle damage.

    If you have joint or muscle pain while taking an aromatase inhibitor, talk with your health care provider. Anti-inflammatory medications (such as aspirin or ibuprofen), special exercises or acupuncture may ease the pain [75-76]. Or, your provider may switch you to another aromatase inhibitor (you may have less pain with a different drug) or recommend tamoxifen [77].

    Bone health

    Aromatase inhibitors cause a loss of bone density, which leads to higher rates of osteoporosis and bone fractures compared to tamoxifen [73]. Some medications may help prevent osteoporosis. Your health care provider may prescribe drugs called bisphosphonates or the drug denosumab to help maintain bone density while you are taking aromatase inhibitors.

    Although mostly a concern for people with metastatic breast cancer who take higher doses of bisphosphonates or denosumab, these drugs can cause severe bone, joint and muscle pain [73,78]. If you have any of these symptoms, report them to your provider right away.

    In rare cases, a serious jawbone disorder called osteonecrosis may occur [51-52]. So, it is important to have a full dental exam before starting treatment and to talk with your provider before getting any dental procedure while you are on bisphosphonates [52].

    Regular exercise can help strengthen and protect your bones [79]. For example, weight-bearing exercise (exercise that involves standing rather than sitting) helps protect bones and lowers the risk of hip fractures [80]. Getting enough calcium and vitamin D (your provider can tell you if you are getting enough calcium and vitamin D) and not smoking can also help strengthen your bones [79].

    Menopausal symptoms

    Hot flashes and night sweats are common in women who take aromatase inhibitors [66]. Although these symptoms may become less frequent and less intense over time, they can still be hard to manage.

    Vaginal dryness is also common in women who take aromatase inhibitors [66]. Unlike hot flashes, vaginal symptoms tend to become worse over time.

    If you have any symptoms, talk with your health care provider. He/she can help treat many of them.

    Learn more about treating menopausal symptoms.

    Side effects of aromatase inhibitors versus side effects of tamoxifen

    Although both aromatase inhibitors and tamoxifen can cause menopausal symptoms such as hot flashes, many of their side effects differ (see Figure 5.11 below). Your health care provider can help you treat many of these side effects.    

    Figure 5.11: Side effects of aromatase inhibitors versus side effects of tamoxifen


    Aromatase inhibitors


    Common side effects

    • Hot flashes and night sweats
    • Joint and muscle pain
    • Loss of bone mineral density (may lead to osteoporosis or bone fractures)
    • Loss of sex drive
    • Vaginal dryness or itching
    • Hot flashes and night sweats
    • Loss of sex drive
    • Vaginal discharge
    • Vaginal dryness or itching

    Less common or rare side effects

    • Carpal tunnel syndrome
    • Hair thinning
    • Heart problems
    • Increased blood pressure
    • Increased cholesterol
    • Mood swings and depression  
    • Vaginal bleeding

    Very rare:

    • Blood clots in the large veins (deep vein thrombosis)
    • Blood clots in the lungs (pulmonary emboli)
    • Bone loss (premenopausal women only)
    • Cancer of the uterus (uterine or endometrial cancer)
    • Cataracts
    • Stroke  

    Adapted from select sources [66,68-70].

    Learn more about the side effects of tamoxifen.

    Long-term side effects

    More time is needed to assess the long-term risks and benefits of aromatase inhibitors.


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    Updated 07/29/15


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