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Wednesday, June 25, 2003“We found that long-term use of combined estrogen and progestin hormone-replacement therapy not only doubles cancer risk, but that the magnitude of this risk increases with duration of use,” said Dr. Christopher Li, a researcher at Hutchinson and lead author of the study, published today in The Journal of the American Medical Association. Li and colleagues found that women over age 65 who take combined hormone-replacement therapy for five to 15 years or for 15 or more years, whether they take progestin sequentially or continuously, face double the breast-cancer risk of other women. Double the risk. That sounds frightening. And the authors of the study put it just as alarmingly in their conclusion: This report provides randomized clinical trial evidence that postmenopausal estrogen plus progestin use significantly increases the incidence of breast cancer within a 5-year period. But, on closer examination, it’s obvious they mean statistically significant, not really significant. And that claim in the popular press that it doubles the risk is also dubious. The study participants were divided into two groups. 8506 took a pill that combined estrogen and progesterone, and 8102 took a placebo for five years. In the first group, 245 (2.8%) developed breast cancer by the end of five years. In the placebo group, 185 (2.2%) developed breast cancer. That’s a difference in incidence of 0.6%. To get the “double the risk”, the authors turned to hazards ratios to magnify the difference. Trouble is, even using hazards ratios, the difference isn’t very impressive. Here are the graphs for the hazard ratio data. Notice how the lines representing the placebo and the treatment groups cross? That’s usually a sure sign that the difference between them isn’t truly significant. There does, however, seem to be a diffference between the two groups in the interpretability of their mammograms. By the end of the study, women who took estrogen and progesterone had higher rates of ambiguous mammogram results. 31.5% of treated women had an abnormal mammogram sometime during the five years of the study compared to only 21.2% of women in the placebo group. Most of those just required a follow-up mammogram to make sure the findings were benign. Suspiciously abnormal mammograms that required a biopsy or were suggestive of malignancy occurred at similar rates in the two groups, the incidence varying by 2% for suspicious lesions (cancer chances = maybe yes, maybe no) and 0.2% for lesions that looked like cancer (cancer chances = higher yes than no). Which leaves one wondering. Is the very slight increase in cancer incidence among the hormone therapy users due to the hormones actually causing the cancer at a cellular level, or is it because they make the breast tissue denser, thus making mammograms harder to interpret, thus resulting in more biopsies and earlier detection. If the study had gone on for ten or twenty years, would the rates of cancer have been the same? Either way, the very small difference in cancer rates between the two groups still isn’t enough to take hormone replacement therapy away from those women who want to use it. Yet, you can bet that's exactly how the data will be used. posted by Sydney on 6/25/2003 08:37:00 AM 0 comments 0 Comments: |
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