Bitter Medicine: Pharmaceutical Listings in the Report on Carcinogens

The National Toxicology Program (NTP) Report on Carcinogens is technically a hazard identification document, which only looks at the potential of a substance to cause cancer at any dose. It assumes that there are no thresholds of exposure below which there will be no cancer effect, and, in fact, it does not deal with exposure - the other component of risk - at all. Mere consideration of a substance in a draft NTP Report has the potential to alarm the public, even where risks may be very low or non-existent due to little exposure to the population. This can rapidly lead to legislative and regulatory actions at the local level.

In addition, sometimes there are significant benefits associated with the substances under consideration for the NTP Report which may outweigh the potential cancer risks. Discussion of benefits is also absent from the Report on Carcinogens. That is why there have been calls for a separate category in the NTP Report for pharmaceuticals. The U.S. Food and Drug Administration (FDA) has endorsed this approach.

One example which demonstrates the need for a separate pharmaceutical category was provided at the October 21, 1999 NTP Public Meeting on the Report on Carcinogens. A member of the audience from a drug company raised the issue of tamoxifen, a key breast cancer drug which his company produces. The drug is primarily prescribed to women at high risk for breast cancer and breast cancer survivors. It was stated that use of tamoxifen, which has been on the market for about 20 years, saw a precipitous decline in western states a few years ago, by about 30,000 patients. This decline was largely attributed to action by the International Agency for Research on Cancer (IARC) in classifying tamoxifen as a cause of endometrial cancer in a small number of cases. Tamoxifen went on to become a major issue related to California Proposition 65, a state-level measure designed to make the public aware of cancer-causing substances.

This action scared away a large number of women, many of whom did not even consult their physicians before stopping their use of tamoxifen. These measures did not provide adequate information on the benefits associated with use of pharmaceuticals such as tamoxifen. The fact that the FDA approved the drug makes the overall case that benefits have been determined to outweigh the risks. If one considers Tamoxifen to have an efficacy rate of 35-50%, then 10,000 to 15,000 women were put at risk of not having the appropriate therapy.

According to the source at the NTP meeting, the FDA Deputy Commissioner has sent a document to the State Department calling for a separate pharmaceutical category on an international basis, not just at NTP. Such new category would provide a much fuller explanation of the risk and benefits of covered drug products, which would allow the public to make better informed decisions.

NTP is currently poised to list tamoxifen as a Known Human Carcinogen in its Ninth Report on Carcinogens. NTP should listen to FDA and create a separate category for products such as pharmaceuticals, where benefits of such substances outweigh their potential for adverse effects. If NTP holds off on the tamoxifen listing, it may be possible to prevent another health mistake on a national scale.