Million Women Study Wrong, Group Says - in Endocrinology, Menopause from MedPage Today

"A study long used to establish causal links between hormone replacement therapy (HRT) and breast cancer is severely flawed, a group of epidemiologists have charged. The observational Million Women Study (MWS), conducted in the U.K., doesn't adequately satisfy several criteria for causality -- including information bias, detection bias, and biological plausibility -- and thus can't be used to conclude that HRT causes breast cancer, according to Samuel Shapiro, PhD, of the University of Cape Town in South Africa, and colleagues.
"HRT may or may not increase the risk of breast cancer, but the MWS did not establish that it does," they wrote in the Journal of Family Planning and Reproductive Healthcare.
Several experts not involved in the study, however, have emphasized that they're well aware of the limitations of observational studies such as the MWS, and that the totality of evidence thus far has shown a strong association between HRT and breast cancer....."

"The analysis of the Million Women Study is the latest in a series of four papers by the Shapiro group exploring the credibility of three studies -- the MWS, the Women's Health Initiative (WHI), and the collaborative reanalysis (CR) -- that causally linking HRT, particularly estrogen plus progestogen therapy, with breast cancer.
The earlier papers similarly found that neither the CR nor the WHI could satisfy criteria for establishing causality...."