Tamoxifen (Nolvadex) and Fareston FAQs: Hormone Therapies to Prevent Breast Cancer Recurrence

Q. I was diagnosed with ER-receptive breast cancer and have had a lumpectomy and radiation. Now my oncologist has prescribed tamoxifen. I think I understand what it’s supposed to do, but I’m not sure…

A. Tamoxifen (Nolvadex) is one of the most common drugs – perhaps THE most common drug – prescribed as a part of the hormone therapy used to prevent breast cancer (either an initial diagnosis, or recurrence). It’s known as a SERM (short for selective estrogen-receptor modulator, should you ever hear the term thrown around). SERMS, which also include raloxifene (Evista) and Fareston (toremifene) work by blocking estrogen from attaching itself to the special receptors on cancer cells. Think of a department store parking lot during a big sale: there are plenty of parking places, but they’re all full, so you’re forced to drive away. A SERM “fills” a cell’s estrogen receptors, leaving no room for estrogen. Breast cancer cells deprived of their estrogen go dormant, and almost always eventually die; some even die immediately.

Fareston (toremifene), a much newer drug than tamoxifen, works in a similar fashion and has similar side effects, with one exception: it doesn’t put a woman at increased risk for endometrial cancer, as tamoxifen does. Since it’s so new, and has thus far been FDA-approved only for postmenopausal women battling metastatic breast cancer, it’s not nearly as common in this country as tamoxifen.

Tamoxifen has been on the market for 30 years, and is considered the “gold standard” of SERMS in particular, and hormone therapy in general. About 70% of women with breast cancer have a type that depends on female sex hormones–estrogen or progesterone–to grow. Reduce the amount of those hormones in your body (and/or prevent the cancer cells from accessing them), and you slow or stop the growth of cancer.

Thirty years ago, tamoxifen was only prescribed for women with advanced breast cancer. In the ’80s, it was given to women who’d been treated for invasive cancer, as a recurrence preventive. By the year 2000, tamoxifen had evolved into the preferred drug for women with early stage, non-invasive cancer, to prevent that non-invasive cancer from coming back in more aggressive form. It’s also now FDA-approved as a preventive in women who’ve never had breast cancer, but are at high risk.

Q. Well, that sounds good. But there has to be a catch. Is tamoxifen 100% effective?

A. Unfortunately, there’s no cancer treatment that’s 100% guaranteed. Despite all we know about it, life is ultimately a mystery. Researchers are making huge gains, but the biology of cancer still includes a lot of unknowns; if it didn’t, we’d have a cure. Nevertheless, statistically speaking, taking tamoxifen for 5 years has been shown to reduce a woman’s risk of recurrence by 40%, and her risk of death from breast cancer by 30%, vs. no hormone therapy. In addition, the risk of developing a new cancer in the opposite breast is reduced by about half. And when you’re talking a possible life-or-death situation, that’s pretty significant.