A new study of 3,823 post-menopausal women found that continuous combined hormone therapy(estrogen combined with 25 to 31 days per month of progestin use) was associated with an increased breast cancer risk among current users of the regimen who had been taking it for five or more years. The study however did not find any association between use of continuous combined hormone therapy and breast cancer risk. This indicated that the increased risk associated with continuous combined HT use dissipates quickly once use is discontinued.
The study which was a multi center, population-based, case-control study was conducted in five U.S. metropolitan areas from 1994 to 1998 and analyzed 1,870 women diagnosed with invasive or in situ breast cancer and 1,953 controls, aged 35 to 64 years. The study looked at pill and patch hormone users as well as several types of hormone regimens. Researchers of the study concluded that there was no association between breast cancer risk and the regimens of either estrogen-alone therapy or sequential HT (estrogen combined with 5-14 days per month of progestin use).