Most at-risk women ineligible for tamoxifen therapy.(Gynecology)

Tamoxifen probably won't prevent many cases of breast cancer in women at risk for the disease because most are ineligible for treatment and those most likely to be eligible are the least likely to develop cancer, according to Carmen L. Lewis, M.D., of the University of North Carolina at Chapel Hill and colleagues.

Of 605 women studied, more than 90% of those found to be at risk for developing breast cancer (based on their responses to a questionnaire about their health and family history) would be ruled out for chemoprevention with tamoxifen due to the risk of adverse events such as blood clots and stroke associated with the drug, the investigators found.

Using the Gail model, they estimated that the percentage of white women in the study with an increased 5-year breast cancer risk (defined as a risk of at least 1.66%) was 9% among those in their 40s, 24% among those in their 50s, and 53% of those in their 60s. Among black women, 3% of those in their 40s, 7% of those in their 50s, and 13% of those in their 60s had this level of risk.

In a hypothetical cohort of 10,000 women similar to those in the study--calculations were made only for white women due to the small number of black women in the study--only 7% of those in their 40s, 6% of those in their 50s, and 10% of those in their 60s met the requirement for discussions about tamoxifen. It is recommended that discussion about chemoprevention take place only with those who have a high potential of benefit and a low potential of harm from using tamoxifen.

Using the same hypothetical cohort, and assuming that tamoxifen would result in a 49% reduction in the number of invasive breast cancers in high-risk women as demonstrated in the 1998 placebo-controlled National Surgical Adjuvant Breast and Bowel Project (NSABP) Breast Cancer Prevention Trial, a maximum of only 6%-8% of ...