Of these factors, only ERT and high body mass were found to increase the risk of breast cancer. Harris and his research group conducted the case-control study using personal interviews with 604 women who were newly diagnosed with breast cancer, and 520 closely matched control patients who had no history of breast cancer. The women were interviewed upon admission to a collaborating hospital in New York City. Their median age was 55. These, in turn, were subdivided into weight groups according to whether they were lean, medium, or heavy in terms of body mass.
Body mass is a measure of weight as related to height.
Those using ERT were also grouped according to whether they'd taken the therapy for more than five years or less than five years. Our results are likely to sharpen that debate. Harris noted that most previous studies have looked at ERT use by women without regard for body mass, so an increase in risk wasn't apparent. Our study differed from most others in that we stratified the women according to body mass. What's more, the study showed that the risk was equally high whether the women had taken ERT for more than five years or less than five years.