Li, the lead author, is a postdoctoral fellow at Hutchinson's public health sciences division. We're still trying to figure out what all the risks are for breast cancer. The two studies are among the first to examine different types of breast cancer and hormone treatments. A new Hutchinson hormone treatment study will cover about 450 cases of each type of breast cancer over five years, Li said. About 85 percent of breast cancer cases are in the ducts that carry milk to the nipple.
Lobular cancer occurs in the milk-producing lobules.
About 8.6 million U.S. women in the United States take the combination treatment and 12 million take estrogen alone. The hormones reduce the risk of broken bones from osteoporosis and ease menopausal symptoms, including hot flashes, vaginal dryness and insomnia. In women who have not had a hysterectomy, progestin is used to lower the risk of endometrial cancer from taking estrogen supplements alone. Earlier studies, including two this year, indicated a heightened risk of breast cancer among women using combination hormone therapy for at least five years but not among those using estrogen alone. Scientists found a 2.6-fold higher incidence of lobular breast cancer in women who took the combination therapy for at least six months and an average of four years.