Georgetown University Medical Center -- Denver, Colo. – Many studies determine hormone levels in the blood as a marker of breast cancer risk. But it hasn’t been known whether these blood tests reflect what is happening in the breast tissue, where certain hormones fuel cancer. Researchers at Georgetown University Medical Center’s (GUMC) Lombardi Comprehensive Cancer Center found that measuring the levels of four hormones in blood known to be linked to breast cancer doesn’t necessarily reflect the levels of these hormones in the breast tissue itself.