Aromatase Inhibitors List: Essential Tools in Cancer Hormone Therapy
Key takeaways:
Aromatase inhibitors are prescription medications used to treat hormone-positive breast cancer in postmenopausal women. Three aromatase inhibitors are available: anastrozole (Arimidex), letrozole (Femara), and exemestane (Aromasin).
All three aromatase inhibitors are similarly effective for treating breast cancer. Anastrozole and exemestane (but not letrozole) are also effective at lowering the chance of breast cancer in those at high risk for it.
Common aromatase inhibitor side effects include hot flashes, vaginal dryness, and muscle or joint pain. Don’t stop taking an aromatase inhibitor on your own. Often, your prescriber can treat your side effects or switch you to a different medication to manage them.
There are many ways to save on aromatase inhibitors. GoodRx can help you navigate your options, which may include GoodRx discounts, copay savings cards, and patient assistance programs. You can find aromatase inhibitor prices as low as $6.48 per month with a free GoodRx discount.
Access savings on related medications
Table of contents
It’s estimated that 2 out of 3 breast cancers are hormone positive. Hormone-positive breast cancer is a type of cancer that has receptors (binding sites) for hormones. When hormones such as estrogen bind with these receptors, it fuels the cancer and helps it grow. So hormone-positive breast cancer is treated with medications that either lower hormone levels or block the hormone receptors.
Aromatase inhibitors are a class of medications that lower estrogen levels to treat and prevent certain breast cancers. But which medications are aromatase inhibitors, and what’s the difference between them?
1. Anastrozole (Arimidex)
Anastrozole (Arimidex) was the first aromatase inhibitor approved by the FDA in 1995.
What it’s prescribed for
Anastrozole is typically prescribed to treat hormone-positive breast cancer in women who have gone through menopause. It’s usually prescribed after surgery to help reduce the risk of breast cancer returning. This is known as adjuvant therapy.
If your cancer has spread beyond the breast, anastrozole is often prescribed along with other medications. It’s also sometimes prescribed for advanced breast cancer in postmenopausal women if the hormone status is unknown. But this isn’t as common.
Anastrozole also has some common off-label uses. You may take anastrozole before surgery to help make the cancer smaller and easier to remove (known as neoadjuvant therapy). Some women at high risk for breast cancer take anastrozole to lower their cancer risk. This is known as chemoprevention.
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In addition, anastrozole is sometimes prescribed for breast cancer in women with ovaries who haven’t gone through menopause. But more steps are needed to block the estrogen produced by the ovaries in this case. Sometimes, the ovaries are removed before treatment. Other times, you’ll take another medication that stops the ovaries from producing estrogen, such as goserelin (Zoladex). Men taking anastrozole for breast cancer will also need to take one of these medications to turn off hormone production by the testicles.
Finally, anastrozole is also used off-label to treat certain forms of infertility in men.
How it works
Aromatase is an enzyme (protein) that helps make estrogen in the body. Anastrozole and other aromatase inhibitors block this enzyme, which stops the production of estrogen. But they only block aromatase in fat tissue, which is where most estrogen is made after menopause.
Aromatase inhibitors don’t affect estrogen made by the ovaries, which is where most estrogen comes from before menopause. So they aren’t an effective treatment option on their own for women who haven’t gone through menopause.
Dosage
Anastrozole comes in a 1 mg oral tablet. It’s taken once daily, with or without food. There’s no dosage adjustment needed for liver or kidney problems.
If you’re taking anastrozole to treat breast cancer, you’ll likely continue treatment for at least 5 years. In some cases, you may take it for up to 10 years. Your oncologist will weigh the risks and benefits along with your personal health history to determine the best treatment length for you. They may also recommend genetic testing to learn more about your cancer risks.
If your breast cancer has spread to other parts of the body or it has returned after a different treatment, you’ll likely continue taking anastrozole until it stops working or the side effects become bothersome.
Experts recommend taking anastrozole daily for 5 years if it's being used for chemoprevention.
How to save on anastrozole
There are ways to save on Arimidex, which is available as a generic- and brand-name medication. GoodRx can help you navigate between GoodRx coupons and copay savings cards to save money on your prescription.
Save with GoodRx: Anyone with a valid prescription, regardless of insurance status, can use GoodRx to purchase a 30-day supply of Arimidex at an exclusive cash price of $298.80. You can also pay as little as $6.48 for an equivalent supply of the generic.
Save with a copay savings card: If you have insurance, you may be eligible to pay as little as $60 (30-day supply) or $180 (90-day supply) for Arimidex using the manufacturer’s Arimidex Patient Direct program. This program also offers home delivery.
Breast cancer prevention: If you’re at high risk for breast cancer, or you’ve had it in the past, these medications can help reduce your future cancer risk.
Aromatase inhibitor side effects: Learn what side effects to expect while you’re taking an aromatase inhibitor and when to be concerned.
Living with breast cancer: Read a first-hand account of one person’s breast cancer journey and the unexpected gifts she found along the way.
2. Letrozole (Femara)
Letrozole (Femara) was the second aromatase inhibitor approved by the FDA in 1997. It works the same way as anastrozole — by blocking aromatase from forming estrogen in women who’ve gone through menopause.
What it’s prescribed for
Letrozole is prescribed for the same indications as anastrozole when it comes to breast cancer, with one exception. Studies haven’t shown that letrozole lowers the risk of breast cancer in women at high risk for it. Only the other two aromatase inhibitors have been shown effective in clinical studies for this use. So letrozole isn’t typically prescribed for chemoprevention.
Letrozole is also commonly used off-label for infertility in women. It’s often prescribed to help with ovulation (when the ovary releases an egg) as part of infertility treatment.
Dosage
Letrozole comes in 2.5 mg tablets. The usual letrozole dosage for breast cancer is one tablet (2.5 mg) taken once daily, with or without food. As with anastrozole, in most cases you’ll take letrozole for 5 to 10 years.
If you have liver problems, you may need to take it every other day (instead of every day). Your prescriber will let you know if this applies to you.
How to save on letrozole
Letrozole is available as both a brand-name and generic medication. Generic letrozole’s price at certain pharmacies is less than $7.80 for a 30-day supply with a free GoodRx discount.
3. Exemestane (Aromasin)
Exemestane (Aromasin) is the third aromatase inhibitor. It was FDA approved in 1999.
What it’s prescribed for
Exemestane is only approved for hormone-positive breast cancer in postmenopausal women who have tried a medication called tamoxifen first.
But it’s often prescribed off-label as a treatment for early breast cancer before or after surgery. And it’s also used for chemoprevention as well as to treat breast cancer in premenopausal women.
How it works
Exemestane works similarly to anastrozole and letrozole, but it’s slightly different. Exemestane is a “steroidal” aromatase inhibitor. It binds more directly to hormone receptors and acts like a group of steroids (hormones) known as androgens in the body.
So far, there doesn’t seem to be any added benefit from exemestane’s steroidal effects when it comes to treating breast cancer. But it does seem to help exemestane cause fewer side effects than anastrozole or letrozole (more on that later).
Dosage
Exemestane comes in a 25 mg oral tablet. The usual dosage is one tablet (25 mg) once daily with food. This is a notable difference from anastrozole and letrozole, which can be taken with or without food.
If you’ve already taken tamoxifen, in most cases you’ll only need to take exemestane until you reach at least 5 total years of treatment. Otherwise, you’ll need to take exemestane for 5 to 10 years or until it stops working, similar to the other medications in this class.
How to save on exemestane
There are several ways to save on exemestane, which is available as both a brand-name and generic medication.
Save with GoodRx. Generic exemestane’s price at certain pharmacies is less than $16.20 with a free GoodRx discount.
Save with a copay savings card. If you have commercial insurance, you may be eligible to pay as little as $4 per month for brand-name Aromasin using a savings card from the manufacturer.
Save with patient assistance programs. If you’re uninsured or underinsured, you may be eligible for Aromasin’s patient assistance program, which offers the medication free of cost.
Which aromatase inhibitor is the most effective?
Studies show that all three aromatase inhibitors are similarly effective when it comes to treating breast cancer. Exemestane may also be effective if you take it after anastrozole or letrozole stops working. That’s because, as mentioned, it works a bit differently than the other two aromatase inhibitors.
When choosing between aromatase inhibitors, your oncologist will decide which to prescribe based on your medical history.
What are the side effects of aromatase inhibitors?
Since they lower the amount of estrogen in the body, the most common side effects of aromatase inhibitors are similar to menopause symptoms. These include:
Hot flashes
Vaginal dryness
Night sweats
Trouble sleeping
Joint and muscle pain
Aromatase inhibitors can also cause joint and muscle pain. This is the most common reason people stop taking their medication. Be sure to let your prescriber know if you’re experiencing bothersome pain while taking an aromatase inhibitor. In some cases, you may need to switch to a different aromatase inhibitor or take a short break from treatment.
Serious side effects
More serious aromatase inhibitor side effects include:
Bone loss
Increased cholesterol levels
Liver problems
Exemestane seems to have a lower risk of bone loss and high cholesterol levels than the other aromatase inhibitors. But in most cases these side effects are something your oncologist will keep an eye out for throughout your treatment.
Good to know: If you experience side effects from an aromatase inhibitor, do not stop taking your medication. This significantly raises the risk that your cancer will return. Talk to your oncologist about any symptoms you’re experiencing. They’ll be able to help manage them without stopping treatment.
The bottom line
Aromatase inhibitors are medications that treat hormone-positive breast cancer in postmenopausal women. The three FDA-approved aromatase inhibitors are anastrozole (Arimidex), letrozole (Femara), and exemestane (Aromasin). In most cases, you’ll take one of these medications for 5 to 10 years as part of your breast cancer treatment.
All aromatase inhibitors are similarly effective for treating breast cancer. The most common side effects are hot flashes, night sweats, and muscle or joint pain. Your oncologist will help decide if an aromatase inhibitor is a safe and effective treatment option for you.
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