Using postmenopausal hormone therapy for more than 15 years increases a woman's risk of developing breast cancer, particularly among leaner women according to research at the Keck School of Medicine of the University of Southern California (USC).
An analysis of the California Teachers Study focused on postmenopausal hormone therapy use among more than 55,000 women for nearly 10 years. The research was conducted by a team including first author Tanmai Saxena, an M.D. Ph.D student at the Keck School. The research was published in the journal Cancer Epidemiology, Biomarkers and Prevention.
Compared with women who never used postmenopausal hormone therapy, women who used estrogen therapy for more than 15 years were at a 19 percent increased risk of breast cancer. The risk was even more pronounced for women who used combined therapy with estrogen plus progestin for 15 or more years. These women had an increased risk of 83 percent, Saxena said.
"This study shows that there needs to be a personalized conversation with women about the risks of using postmenopausal hormone therapy," said Saxena. "Different women appear to have different risks from hormones."
Thinner women who go on hormone therapy also appear to be at higher risk, Saxena said.
The research revealed that body mass index (BMI) may be an indicator of breast cancer risk for women who use postmenopausal hormone therapy. Women with a BMI of 30 or less appear to be at increased risk of breast cancer from combined therapy, while women with a BMI of 30 or higher were at less risk. Women with a BMI of 25 or less were at the highest risk.
The purpose of the study was to elaborate on the Women's Health Initiative findings regarding the effects of postmenopausal hormone therapy on breast cancer risk. The 15-year WHI, conducted by the National Institutes of Health, was halted in 2002 after increased risks of cardiovascular disease and breast cancer were found among women who were taking combination therapy as part of the trial. This study looked at the risk associated with particular formulations of combination hormone therapy as well as the subtypes of breast cancer resulting.
Cancer Epidemiology, Biomarkers and Prevention, August 10, 2010
University of Southern California (http://www.usc.edu)