What is tamoxifen derived from? How could the FDA approve this drug when it has such serious side effects?

Louise

Tamoxifen (Nolvadex) is a synthetic substance that is an anti-estrogen in the breast. It has been used for about 20 years as chemotherapy (drug treatment) for advanced breast cancer and more recently to prevent recurrence of early-stage breast cancer treated by lumpectomy. The Breast Cancer Prevention Trial recently examined tamoxifen's usefulness in preventing first breast cancers in women who are at high risk; this study found a 45 percent reduction in the development of breast cancer in the group on tamoxifen, and tamoxifen has been approved for this use as well.

It is true that tamoxifen has potentially serious side effects. There is a small increase in blood clots, especially in women who are undergoing other forms of chemotherapy. It may increase the chance of developing cataracts, but as with blood clots, this risk is small. Tamoxifen, while acting as an anti-estrogen in breast tissue, acts like estrogen on the uterine lining; this increases the risk of developing cancer of the uterine lining by two to three times. This is the same increase in uterine cancer that is seen in women with a uterus who take estrogen replacement without a progestin. Any woman on tamoxifen who has any abnormal vaginal bleeding or pelvic pain must be evaluated by her gynecologist! Other side effects are less serious, but may be annoying: hot flashes, irregular periods, vaginal dryness.

Tamoxifen was approved by the FDA a long time ago to treat breast cancer, and only recently was that approval expanded to include decreasing the risk of developing breast cancer in a very select group of women at very high risk. As a treatment for advanced breast cancer, or to prevent recurrence of a treated early-stage cancer, tamoxifen has time and time again been proven to save lives. With this drug, many more women are able to survive their breast cancer than will develop blood clots, cataracts or uterine cancer. As far as using tamoxifen to potentially prevent breast cancer, that is a highly individual decision that must be carefully considered by each women and her doctor, after complete discussion of her risk factors and all possible drawbacks to tamoxifen therapy.