Aromatase inhibitors are hormone therapies that are used to treat women with hormone sensitive tumors. (ER+ and/or PR+) Aromatase inhibitors work by blocking the aromatase enzyme, which converts androgens into estrogen. A woman must be postmenopausal to benefit from an aromatase inhibitor. That’s because postmenopausal women get most of their estrogen from the conversion of androgens into estrogen by the aromatase enzyme. In contrast, premenopausal women get most of their estrogen directly from their ovaries (and aromatase inhibitors aren’t able to block this estrogen).

Currently three aromatase inhibitors are approved for use by the U.S. Food and Drug Administration (FDA): anastrozole (Arimidex), letrozole ( Femara), and exemestane (Aromasin). These drugs are the standard of care for postmenopausal women, while tamoxifen remains the standard of care for premenopausal women. For a premenopausal (still menstruating post chemotherapy) woman to take an aromatase inhibitor, she must have her ovaries removed (oophorectomy) or take a drug that will suppress ovarian functioning and decrease estrogen levels, putting her into menopause. The drugs most commonly used for this purpose are goserelin (Zoladex), leuprolide (Lupron), and triptorelin (Trelstar).

In 2003, The International Breast Cancer Study Group (IBCSG) launched two large randomized phase III trials, called TEXT and SOFT, to look at whether it was better for premenopausal women to take tamoxifen or the AI exemestane (Aromasin). These trials also looked at if using tamoxifen along with ovarian suppression was better than tamoxifen alone. The findings from these studies, announced in 2014, suggested that exemestane along with ovarian suppression was more effective than tamoxifen along with ovarian suppression in preventing recurrence. However, at this point in time, no difference was seen in overall survival. The women in the study will need to be followed longer to get that information. But the study also showed that some premenopausal women with hormone-sensitive tumors have an excellent prognosis with tamoxifen alone. So, it goes back to you, as an individual, and your specific tumor. If your doctor feels that you are at higher than average risk for recurrence (in general, this includes women 35 and younger and women who needed chemotherapy in addition to hormone therapy) ovarian suppression and exemestane (Aromasin) should be an option you discuss with your doctor.

If you are not at higher risk of recurrence, you will want to think about the side effects of ovarian suppression. These drugs (or having your ovaries removed) puts you into immediate menopause and you are likely to experience many of the side effects that go with it, such as hot flashes, night sweats, and vaginal dryness. You can learn more about how to manage these symptoms here.

Another thing to consider if you are premenopausal is that, depending on your age, it is possible that while you are on tamoxifen, you may become menopausal. At that point, it will be important for you to talk with your doctor about whether you should switch from tamoxifen to an aromatase inhibitor.

If you do decide to use an AI as adjuvant therapy, you should have your bone density monitored during your treatment. Some oncologists recommend that premenopausal women try to decrease their risk of bone loss by also taking a bisphosphonate, a drug used to treat osteoporosis. You should speak with your oncologist about this as well. Whether you take tamoxifen or an AI, you should to try to maintain your bone health by doing weight-bearing exercises. You also need make sure that you get adequate amounts of vitamin D and calcium in your diet, taking supplements if necessary.