(Seattle-AP) - Women who take hormone-replacement therapy with estrogen and progestin may more than double their risk of a form of breast cancer. Researchers in Seattle say they found a more than two-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. In a related study, scientists found that lobular cancer has increased nationwide since the 1980's, when the combination estrogen-progestin treatment gained widespread use. About 85% of invasive breast cancer cases are in the ducts that carry milk to the nipple. Lobular cancer occurs in the milk-producing lobules and accounts for between 5% and 10% of breast cancer cases. Results of the two new studies appear Thursday in the journal Cancer.