Cancer experts debate tamoxifen

Vegetarian Times, July, 1996 by Ben Lilliston

Skyrocketing breast cancer rates over the last decade--up 42 percent since 1986--have turned this disease into a sensitive political issue. As a result, scientific researchers have been frantically searching for ways to prevent breast cancer, which will afflict one out of nine American women over the course of a lifetime. Experts are divided as to why breast cancer rates seem to be rising; factors such as the aging population and better detection methods certainly play a role. But sharp questions are being raised about a research trial using healthy women to test a breast cancer prevention drug that has been found to cause another type of cancer.

This controversy surrounds tamoxifen, one of the world's most widely used breast cancer treatment drugs. In 1992, the National Cancer Institute (NCI) began a 10-year, $68 million study--one of the largest prevention trials ever launched--to see if the drug can prevent breast cancer in healthy women. But in February, The World Health Organization (WHO) formally designated tamoxifen as a human carcinogen because its use has been linked to sharply elevated risk of endometrial cancer, a malignancy of the uterine lining. Other evidence indicates that tamoxifen enhances one's risk of contracting liver cancer.

In response, cancer experts and women's health advocates have been calling on the NCI to stop tamoxifen chemopreventive trials--which test the drug's ability to prevent disease--on healthy women, and to look more carefully at environmental and dietary roles in causing cancer. Samuel Epstein, M.D., a professor at the School of Public Health at the University of Illinois at Chicago and chairman of the Chicago-based Cancer Prevention Coalition, takes issue with the NCI's decision to use a possible carcinogen as a cancer prevention trial: "This is an example of NCI's indifference and ignorance of fundamental principles of preventing cancer--breast cancer in particular." He believes that cancer rates are going up because of exposure to synthetic chemicals in food additives and industrial pollution, and that breast cancer patients would be better served by research investigating the widespread presence of carcinogens in the air and water. "Using a potentially risky agent [on healthy women] is in my opinion a radical shift in biological sanity," agrees Keith Block, M.D., a Chicago-based nutritional oncologist who does treat women who have been diagnosed with breast cancer with tamoxifen, but does not use it to prevent cancer in at-risk patients. "Are we taking women and putting them through a potentially fatal cancer experiment?"

Cindy Pearson, program director of the National Women's Health Network, a Washington, D.C.-based women's health advocacy group, also wants the NCI to shift its research priorities. "We would love to see the NCI look at causes of breast cancer, and ways women can reduce their risks," she says. These include research on a very low-fat diet, exercise, exposure to environmental chemicals and X-ray radiation, and new evidence linking vitamin and mineral supplements, such as selenium, with lower rates of breast cancer. "For far too long we have been a culture bringing ambulances to the bottom of the cliff, instead of putting guardrails at the top," Block adds.

But the NCI stands by the tamoxifen study. Program director Karen Johnson says their scientists have reviewed the same body of evidence as WHO, and have concluded that the benefits outweigh the risks. The agency estimates that out of 8,000 women, tamoxifen will prevent 13 3 cases of breast cancer, while causing 83 cases of endometrial cancer--which has a lower mortality rate than breast cancer. Pearson and others believe these terrifying odds are the reason 20 percent of the women who originally signed up for the trial have left, and why the NCI is having difficulty enrolling replacements. The NCI responds that attrition rates have not been higher than usual for such studies, and notes that information on risks of getting cancer from tamoxifen are on the consent forms for participants in the trial, which also includes a waiver of compensation for illness.