Deciding on breast cancer treatment: Tamoxifen versus aromatase inhibitors

As the therapies for various cancers expand, physicians find themselves involved in more and more complex decision making and counseling of patients regarding treatment options. For example, take women with so-called hormonally responsive breast cancer. For the woman who is no longer menstruating, and whose tumor characteristics suggest that it will be responsive to a change in the hormonal environment, the treatment choices are either an antiestrogen or an aromatase inhibitor.

How does a woman choose which is right for her? Only through detailed and frank discussion with a physician can a decision be individualized. This decision will take into consideration prior cancers, such as cancer of the uterus, the strength of the woman's bones, and the propensity of forming blood clots.

The below article, first published in the Harvard Health Letter describes some of the treatment options for breast cancer—and the reasons why a woman would opt for one over the other:

Breast cancer is classified according to whether it has receptors for the female hormone estrogen. If the cancer has estrogen receptors — or, as cancer specialists say, it is estrogen-receptor (ER) positive — estrogen can stimulate the cells to grow and divide, resulting in more cancer. About two-thirds of all breast cancers are ER-positive. The good news is that ER-positive tumors tend to be less aggressive than those that are ER-negative, so the prognosis tends to be quite a bit better. Still, blunting the effects of estrogen is important for preventing recurrence.

There are two main types of anti-estrogen medications: tamoxifen (Nolvadex), which blocks the ability of estrogen to stimulate cancer cell growth, and the aromatase inhibitors, which deplete the production of estrogen. The FDA has approved three aromatase inhibitors: anastrozole (Arimidex), exemestane (Aromasin), and letrozole (Femara).

Tamoxifen is effective in both pre- and postmenopausal women, but the aromatase inhibitors are effective only for postmenopausal women. So if you are premenopausal, tamoxifen is really the only choice.

If you're postmenopausal, there's more to think about. For years, the standard recommendation was that women take tamoxifen for five years after surgery. But results from clinical trials have suggested that either an aromatase inhibitor alone from the start, or following two to three years of tamoxifen, may be more effective than the standard five-year tamoxifen regimen.

Both tamoxifen and aromatase inhibitors have side effects. Each can lead to menopausal symptoms like hot flashes and night sweats. Years of data show that tamoxifen can cause blood clots and cancer of the uterus, although rarely so (in less than 1% of patients). The aromatase inhibitors may lead to more profound vaginal dryness and sexual dysfunction, osteoporosis, and an arthritis-like syndrome.

So for postmenopausal women, choosing between tamoxifen and the aromatase inhibitors is complicated and needs to be decided on a case-by-case basis. You and your doctor should discuss these issues as you decide which form of anti-estrogen therapy to select.

How have you gone about making decisions about important medical treatments?

Marc Garnick, M.D., is an internationally renowned expert in medical oncology and urologic cancer, with a special emphasis on prostate cancer. He is a Clinical Professor of Medicine at Harvard Medical School and maintains an active oncology practice at Beth Israel Deaconess Medical Center. Dr. Garnick serves as Editor in Chief of Perspectives on Prostate Diseases, a quarterly report from Harvard Health Publications.

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