In a recent article published online in the Journal of the National Cancer Institute, investigators affiliated with the HABITS (Hormone replacement therapy After Breast cancer -- Is It Safe?) study concluded that hormone replacement therapy was associated with a significantly increased risk of a new breast cancer event in breast cancer survivors.

The investigators analyzed extended follow-up information on over 400 women who were enrolled in the HABITS study, which was stopped early due to suspicions of an increased risk of breast cancer following hormone replacement therapy. Of the 221 breast cancer survivors who were treated with hormone replacement therapy, 39 experienced a recurrence of breast cancer within 4 years. 17 of the 221 breast cancer survivors who did not receive hormones developed a new breast cancer event during the same time period. According to this analysis, hormone replacement therapy was associated with a more than two times greater risk of breast cancer recurrence.

Hormone replacement therapy is also known to increase the risk of first-time breast cancer in healthy women. Further studies are needed to more closely examine the specific types of hormone replacement therapy used, and whether other factors might contribute to the risk of first-time breast cancer and breast cancer recurrence.