Using Femara (Letrozole) to Prevent Breast Cancer Recurrence

Benefits and Side Effects of Aromatase Inhibitors for Breast Cancer

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What do I need to know about the benefits, indications, and side effects of Femara (letrozole) for breast cancer?

What Is Femara (Letrozole)?

Femara (letrozole) (commonly misspelled as fimara, femarra, and femera) is a drug in a category known as aromatase inhibitors.  These drugs block the formation of estrogen made in areas other than the ovaries.  Since estrogen can act as a fuel for the growth of breast cancer, Femara helps to lower your risk of breast cancer recurrence and improves your chance of survival.

If you are coping with side effects from this medication, make sure to read on about the benefits of Femara and ways in which the side effects of this drug can be managed.

Drug Type

Femara is an antiestrogen, or aromatase inhibitor.  Other aromatase inhibitors include Aromasin (exemestane) and Arimidex (anastrozole.) Femara is not a steroid.

Hormone Therapy for Breast Cancer

Studies indicate that using hormone therapy for estrogen receptor positive breast cancer decreases the risk of recurrence and increases survival.  There are two primary types of hormone therapy for people with breast cancer.  Before menopause, the ovaries make the greatest amount of estrogen.  If your ovaries are functioning, Tamoxifen is used to block the ability of estrogen to bind with cancer cells.  After menopause, whether natural menopause or menopause induced by chemotherapy or ovarian suppression medications, the major source of estrogen in the body is that produced from the breakdown of androgens in other locations of the body.

Aromatase inhibitors work to block this reaction which converts androgens to estrogens, thus blocking the formation of estrogen.

How Femara Works to Prevent Breast Cancer Recurrence

After menopause (either natural or that induced by surgery, chemotherapy, or ovarian suppression) the primary source of estrogen in the body is that which is produced in the form of androgens in fatty tissues in the body.

These androgens are converted to estrogen in a reaction catalyzed by an enzyme called aromatase.  By inhibiting the action of aromatase, the production of estrogen is blocked.  This results in less estrogen being available in the body to stimulate any remaining or dormant breast cancer cells.

Femara blocks aromatase, preventing estrogen production and lowering your hormone levels. If breast cancer cells are present in your system, they have much less chance to grow if they can’t get any estrogen.

What Does Research Tell Us About Femara

For women who have estrogen receptor positive breast cancer, and receive adjuvant chemotherapy, treatment with an aromatase inhibitor appears to reduce the risk of recurrence by 50 percent.

Studies looking at women who had received 5 years of Tamoxifen treatment, found that using Femara after this time, even starting a few years later, resulted in improved survival.

Women who become menopausal in the first 2 to 3 years on Tamoxifen therapy and were then switched to Femara for the remainder of 5 years, had a lower risk of recurrence than women who continued to use Tamoxifen alone for a 5 year period.

For women who are menopausal at the onset of hormone treatment, there are more benefits in using aromatase inhibitors initially than beginning with Tamoxifen.

It's not known exactly the ideal length of time that Femara shows a benefit, in other words, whether or not using Femara for a period beyond 5 years is of benefit.  Talk to your oncologist as this area is changing with regard to current recommendations.

Who Can Take Femara

This drug is for women who have been diagnosed with estrogen receptor-positive breast cancer. A patient must have completed primary treatment and be in menopause. Pre-menopausal women can take Femara if their ovaries are chemically suppressed. Women who have had estrogen receptor-negative breast cancer will not benefit from this drug.

Common Side Effects of Femara and Other Aromatase Inhibitors

Femara may cause these side effects:

Call your doctor if you have these symptoms:

Muscle Aches/Side Effects and Discontinuing Treatment

Unfortunately, muscle and joint aches are a very common side effect of treatment with Femara. In one large study it was found that 32 percent of patients discontinued their use of this drug due to side effects.  Nearly 24 percent of people stopped the drug due to muscle and joint aches.  It's important to note that among those who stopped their aromatase inhibitor due to side effects, a third were able to tolerate one of the other medications in this class of drugs.

Talk to your doctor about what you can do to help you cope with joint and muscle aches.  In one controlled trial it was found that acupuncture was more helpful than sham acupuncture in relieving muscle aches due to aromatase inhibitors.

Hot flashes can also be annoying, and are expected since the medications are decreasing the production of estrogen in your body.  Check out these thoughts on ways to cope with hot flashes.

Osteoporosis Prevention

The use of aromatase inhibitors does increase bone loss, and has been noted to not only increase the risk of osteoporosis, but in the number of bone fractures among women who use these drugs.  Talk to your doctor about screening for osteoporosis.  Make sure that you are getting adequate vitamin D and calcium.  In fact, optimal vitamin D levels in your blood or correlated with breast cancer survival, so talk to your doctor about having your vitamin D level tested, and what you can do if the level is low.


The temporary side effects of Femara are much more tolerable when you know that your risk of recurrence is greatly reduced. Women who took Femara after five years of Tamoxifen had significantly lower risk of recurrence that those who took a full five years of Tamoxifen. In addition, with Femara, your risk of a new cancer in the opposite breast is less than with Tamoxifen alone.

Dosing Recommendations

Take Femara once a day with water. This drug does not have to be taken with food. Try to take it at the same time each day, to maintain an even level of the drug in your system. If you miss a dose, don’t double up, just wait till the next day and resume your medication schedule. Do not take this drug if you are still having menstrual periods or are pregnant.

It is available as a 2.5 mg pill, brand name (no generic version available), and prescription only.


Goss, P., Ingle, J., Martino, S. et al. A randomized trial of letrozole in postmenopausal women after five years of tamoxifen therapy for early-stage breast cancer. The New England Journal of Medicine. 2003. 349(19):1793-802.

Halsey, E., Xing, M., and R. Stockley. Acupuncture for joint symptoms related to aromatase inhibitor therapy in postmenopausal women with early-stage breast cancer: a narrative review. Acupuncture in Medicine. 2015. 33:188-195.

Henry, N., Azzouz, F., Desta, A. et al. Predictors of Aromatase Inhibitor Discontinuation as a Result of Treatment-Emergent Symptoms in Early-Stage Breast Cancer. Journal of Clinical Oncology. 2012. 30(9):936-942.

Senkus, E., Kyriakides, S., Ohno, S. et al. Primary breast cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Annals of Oncology. 2015. 26 (suppl 5):v8-v30.

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