Tamoxifen and Breast Cancer

Most of what you hear about tamoxifen is for women who have had breast cancer. But tamoxifen also plays a role for women who are at high risk for breast cancer but who have not been diagnosed with it—and, it is hoped, never will be.

About 29 million women in this country are at high risk for breast cancer, according to the criteria of a major study called the NCI/NSABP Tamoxifen Breast Cancer Prevention Trial. Twenty-six million of these women are considered to be at high risk simply because they are at least 60 years old.

Many of these "high-risk" women are asking themselves and their doctors if they should consider taking tamoxifen. There is finally firm evidence that taking tamoxifen can reduce the risk of breast cancer in these women.

Results of the first Breast Cancer Prevention Trial

A significant step in the fight against breast cancer is the NCI/NSABP Tamoxifen Breast Cancer Prevention Trial Studies. In April 1998, results were announced from this groundbreaking research, with over 13,000 women participating.

Taking tamoxifen was shown to reduce the risk of developing both invasive and non-invasive breast cancers by nearly 50%. The results were revealed fourteen months ahead of schedule (with half of the women having participated in the study for at least four years), because tamoxifen had such a dramatic benefit. Investigators felt it was unethical to withhold this new information about tamoxifen from the study's participants who were taking the placebo (sugar pill).

Background of the study

Only women considered to be at high risk for breast cancer were eligible for the study. (A participant's risk of getting breast cancer during the five-year study period was approximately 3–4%, just under 1% per year. But beyond the five years, as the woman grows older, her yearly risk increases.)

Half of the women took tamoxifen by pill (the same 20-mg dose taken by women who have had breast cancer), and the other half took a placebo (a sugar pill that looked just like the tamoxifen (a placebo)). Neither the woman nor her doctor knew if she was taking the real or fake pill or the placebo, so that expectations didn't influence the results. This is called a double-blind study.

High risk for breast cancer was defined in several ways:

• being at least 60 years old;

• having had a prior breast biopsy showing lobular carcinoma in situ, which is a pattern of breast tissue growth that predicts an increased risk for breast cancer in both breasts; or

• being assessed as high risk for breast cancer in a sophisticated computer calculation that weighs a variety of risk factors.

Other risk factors included:

• having one or more first-degree relatives (mother, sister, or daughter) with breast cancer;

• young age at first menstrual period;

• being 30 or older at delivery of first child, or never having a full-term pregnancy;

• number of prior breast biopsies, particularly if one showed "atypical ductal hyperplasia" (when breast cells start growing in a slightly abnormal way); and

• race—in general, Caucasian women have a higher risk of breast cancer than women of color.

Women were not allowed to take part in the study if they:

• were pregnant, or planning to be during the time of the study (tamoxifen has not been proven safe to take during pregnancy);

• had a prior cancer (other than a minor skin cancer);

• had a history of blood clots that would make them more likely to have adverse effects from tamoxifen.

The women in the study could not take any other form of hormone therapy—such as hormone-replacement therapy for menopause, or birth control pills—during the study. Only about 3% of the women participating in the study were African-American, Asian-American, or Hispanic, despite earnest efforts to recruit a more representative selection of the overall population.

Source: breastcancer.org