gen levels at a single time is linked to breast cancer, but
             no evidence links estrogen levels over an extended time to the risk of breast
             cancer. This what was thought until researchers at the "New England Journal of
             Medicine" proposed a study. Bone mass is a cumulative effect of estrogen on
             bones scientists say, and so the study focused on the more easily observed
             density and mass of bone tissue in women. Four levels were studied, and the
             research was tallied. The risk for getting cancer in the lowest stage of bone
             mass was about 2%, and then 2.6, 2.7, and 7.0 in the second, third, and fourth
             levels of higher mass respectively. This research lent itself to the
             assumption that cumulative exposure to estrogen might play a part in breast
             cancer (Fitzgerald et al, 1996). Other hormonal factors have been viewed as
             potential breast-cancer-causing agents. Birth control pills are thought by
             some to lead to breast cancer. Early birth control pills used much more
             estrogen and progesterone than do today's pills. Lots of contradictory results
             ...