Harvard Women's Health Watch

By the way, doctor: Should I switch from tamoxifen to an aromatase inhibitor?

Q. Two years ago, I had a lumpectomy and radiation for invasive early-stage breast cancer. After that, my oncologist prescribed five years of tamoxifen. But I keep hearing about new drugs that might be better. I'm 60 and long past menopause. Should I switch to one of these newer drugs?

A. You're asking a good question at just the right time in your breast cancer treatment. These days, women like yourself have more choices than they did even a few years ago. Since the 1980s, tamoxifen has been the standard treatment after initial surgery, radiation, and chemotherapy for women whose tumors are fueled by hormones, chiefly estrogen. Five years of tamoxifen reduces the risk of recurrent breast cancer by 47% and the risk of death by 26% in women with early-stage, hormone receptor–positive breast cancer.

Tamoxifen works by attaching to estrogen receptors in breast tissue and blocking the hormone's effects. In other tissues, it mimics estrogen, which can have both good and bad effects. On the positive side, tamoxifen stimulates bone growth, reducing the risk of osteoporosis. But in the uterus, it stimulates the growth of endometrial tissue, increasing the risk of endometrial cancer. It also raises the risk of serious, sometimes fatal, blood clots. Tamoxifen is not recommended for more than five years.

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