Close to 80% of breast cancers are considered hormone receptor-positive (HR-positive). This form of breast cancer relies on hormones such as estrogen and progesterone to grow. HR-positive breast cancers are usually treated with hormone therapies, including aromatase inhibitors and selective estrogen receptor modulators. These medications work by blocking hormone receptors or lowering the amount of estrogen in the body.

Exemestane (Aromasin) is a popular oral aromatase inhibitor that's used to treat HR-positive breast cancer. Understanding how exemestane works, who can take it, and what side effects to expect can help you make an informed decision about your cancer treatment.

Below, we provide answers to eight frequently asked questions about exemestane for breast cancer.

1. What is exemestane used for?

Exemestane is used to treat breast cancer in a few different scenarios. Exemestane is most often used to treat HR-positive breast cancer in women who have completed menopause. In some cases, it's also prescribed to women who are going through premenopause and are receiving ovarian suppression.

Exemestane is generally used as part of adjuvant therapy in women with early-stage breast cancer to reduce the risk of the cancer coming back. Adjuvant therapy lasts at least 5 years and often includes 2 to 3 years of tamoxifen treatment followed by 2 to 3 years of exemestane treatment. Exemestane is also FDA approved to treat advanced breast cancer that has stopped responding to tamoxifen.

2. What happens when you stop taking exemestane?

Adjuvant therapy is considered safe to stop after 5 years overall. This is generally enough time to reduce the risk of the cancer returning. But, depending on your unique situation, your oncology specialist may want you to take exemestane for a longer period of time - especially if you have certain risk factors that make your cancer more likely to return.

If you're taking exemestane to treat advanced breast cancer, you'll likely take the medication until it stops working.

It's important to take exemestane exactly as directed by your oncology specialist for the best outcome. Stopping treatment too early can allow cancer cells to grow back and potentially spread to other parts of the body. Women who stop hormone therapy early are up to 56% more likely to have their cancer come back compared to women who finish their full course of treatment.

Important: If you're thinking about stopping treatment with exemestane due to side effects or other concerns, make sure to talk to your oncology specialist first. They can help you identify solutions - such as lowering your dosage, managing side effects, or exploring alternative treatments - so you can stay on track with your treatment plan and minimize the risk of cancer recurrence.

3. How does exemestane work?

Exemestane works by lowering the amount of estrogen available in the body. It does this by blocking aromatase, which is an enzyme (protein) that's involved in making estrogen and other hormones. Exemestane permanently attaches to aromatase, preventing it from making estrogen.

By lowering the amount of estrogen in the body, exemestane helps inhibit the growth of breast cancer cells.

4. How effective is exemestane for most women?

When taken as prescribed, exemestane is a very effective treatment for many people with HR-positive breast cancer. Studies suggest that taking exemestane for adjuvant therapy after 2 to 3 years of tamoxifen is effective for early-stage breast cancer in postmenopausal women. This is also true for premenopausal women who are receiving ovarian suppression.

One analysis found that after completing 5 years of adjuvant therapy, about 85% of postmenopausal women and 93% of premenopausal women showed no signs or symptoms of breast cancer. Exemestane is particularly beneficial for women at a high risk of recurrence, such as those diagnosed with breast cancer before age 35.

Exemestane is also effective for treating advanced HR-positive breast cancer after tamoxifen has stopped working. Similarly, exemestane can be helpful when paired with everolimus (Afinitor) after other aromatase inhibitors, such as letrozole (Femara) and anastrozole (Arimidex), stop working.

5. Should you take exemestane in the morning or at night?

You can take exemestane in the morning or at night - whichever timing works best for your daily routine. What's more important is that you choose a consistent time to take it every day. You'll also want to make sure to take exemestane with food, which helps your body absorb the medication.

The recommended exemestane dosage is 1 tablet (25 mg) taken once daily after a meal. But your oncology specialist may need to adjust your dosage if you're taking a medication that can interact with exemestane. Phenytoin (Dilantin) and carbamazepine (Tegretol) are examples of medications that can affect how exemestane is broken down in the body.

Be sure to let your oncology specialist know about all of the medications and supplements you take before starting treatment with exemestane.

6. What are the short- and long-term side effects of exemestane?

Exemestane generally has fewer side effects than other aromatase inhibitors. But side effects are still possible.

The potential short-term effects of the medication are similar to menopause symptoms. The most common short-term side effects of exemestane include:

• Hot flashes

• Vaginal dryness

• Headaches

• Nausea

• Fatigue

• Trouble sleeping

Long-term side effects are also possible with exemestane. Some people experience muscle and joint pain around 6 weeks after starting the medication. Over time, exemestane can also cause bone thinning and osteoporosis. People who have a high risk of developing osteoporosis should have their bone mineral density checked before and while taking exemestane.

Heart problems, including heart failure and heart rhythm issues, can also happen with exemestane, especially for people who have taken it for more than 4 years.

7. Can you be in the sun while taking exemestane?

Yes, you can be in the sun while taking exemestane. The medication hasn't been linked to increased sun sensitivity.

Still, as is the case for everyone, it's important to take steps to protect your skin from harmful rays while outdoors:

• Use a broad-spectrum sunscreen with an SPF of 30 or higher.

• Wear protective clothing, including a hat, and sunglasses while outdoors.

• Avoid being outside when the sun's rays are strongest, typically between 10AM-4PM.

If you notice increased skin sensitivity while taking exemestane, talk to your oncology specialist for guidance.

8. Who shouldn't take exemestane?

Premenopausal women who aren't receiving ovarian suppression should avoid taking exemestane. Since the ovaries can still produce estrogen during premenopause, reducing estrogen levels with the medication could inadvertently signal the ovaries to make even more estrogen. This would make exemestane ineffective.

Exemestane can also cause harm to unborn fetuses, so it shouldn't be taken by people who are pregnant. If you haven't experienced menopause and are taking exemestane, you should use effective birth control methods to prevent pregnancy. It's important to take all precautions to avoid becoming pregnant while taking exemestane and up to 1 month after your last dose.

How to save on exemestane

There are ways to save on exemestane, which is available as both a brand-name and generic medication. GoodRx may be able to help you save over 90% off the average retail price of the generic version. Generic exemetane's price at certain pharmacies may be as low as $15.00with a free GoodRx coupon.