Hormone Therapy Raises Ovarian Cancer Risk
Study Shows an Increase in Risk for Estrogen-Only or Estrogen-Plus-Progestin Therapy
July 14, 2009 -- Women who are on hormone therapy or who have used it in the recent past are at higher risk of ovarian cancer than women who have never been on hormone therapy, a new study shows.
The increase in risk was found regardless of the hormone dose or formulation, whether hormones were taken by mouth, transdermal patch, or vaginally, or whether the treatment included just estrogen or estrogen and progestin, the researchers say.
The study confirms earlier research linking hormone therapy and ovarian cancer, but the new study is believed to be the largest and most detailed study to date on the topic, says the study's lead author Lina Morch, a researcher at Rigshospitalet, Copenhagen University in Denmark.
"Our study underlines that postmenopausal hormones increase the risk for ovarian cancer," she tells WebMD in an email interview. "Furthermore, this study suggests that no type of hormone seems safe regarding the risk of ovarian cancer -- even at use below four years the risk is increased." Some previous research had not found an increased cancer risk with hormone use of less than five years.
Both estrogen alone and combination therapy that adds progestin boosted risk, Morch says. Her study is published in The Journal of the American Medical Association.
Ovarian Cancer and Hormones
In the study, Morch and her team evaluated more than 909,000 Danish women, ages 50 to 79, who were on national Danish registers. After an average of eight years of follow-up, 3,068 cases of ovarian cancer were found. At the end of the study, 63% of the women were never-users of hormone therapy and 9% current users.
Compared to never users, current hormone therapy users had an overall 38% increased risk of ovarian cancer.
Put another way: for every 8,300 women on hormone therapy per year, one extra case of ovarian cancer could be attributed to hormone therapy.
Risk did decline in past users as the years of being hormone-free increased. By the time past users had been off hormone therapy for two years, their risk of ovarian cancer was about the same as for non-users, Morch found. By the time women had been off the hormone therapy for more than six years, the risk of ovarian cancer was nearly 40% less in these past users than the never users. Morch says that finding is based on a low number of women who had quit hormone therapy for more than six years. ''What is important is the risk declines in former users with increasing time since last use,'' she says.