According to the American Cancer Society, taking estrogen alone is not linked to a higher risk of breast cancer. In fact, in certain groups of women, such as those with no family history of breast cancer or no personal history of benign breast disease, estrogen may lead to a slightly lower risk of breast cancer.The story is a little different for women taking a combination of estrogen and progestin, however. The Women's Health Initiative found taking estrogen and progestin replacement therapy was linked to a higher risk of breast cancer. Specifically, for every 10,000 women who took estrogen and progestin hormone replacement therapy each year, there were eight more cases of breast cancers than there were in women who hadn't taken the hormones. And the longer a woman took estrogen and progestin replacement, the higher her risk. However, this risk drops within three years of stopping the hormones but remains slightly elevated compared to women who never used combination hormone therapy. The ACS also reports breast cancers in women taking estrogen and progestin replacement therapy tend to be larger and possibly more advanced once they are found.HT can also increase breast density and make mammograms less reliable.