A major US study has found that women who have taken postmenopausal oestrogens for ten years or more are at substantially greater risk of fatal ovarian cancer.
The risk persists for many years after therapy is discontinued, researchers from the American Cancer Society report in the Journal of the American Medical Association.The study followed 201,681 postmenopausal women from 1982 to 1996 and found ERT (oestrogen replacement therapy) increased the risk and this persisted for up to 29 years after women stopped using it.
Twenty two percent of the women in the study had used ERT, including 11,024 who were users at the start of the study (baseline users) and 35,236 who were former users. A total of 944 ovarian cancer deaths were recorded in the 14 year study until December 1996.
Researchers found the risk of death was approximately doubled in women who had used oestrogens for ten or more years within the 15 years prior to enrolment. Annual age-adjusted ovarian cancer death rates per 100,000 women were 64.4 for baseline users with 10 or more years of use, 38.3 for former users with 10 or more years of use, and 26.4 for never users.
Women who were using ERT at baseline had 51 percent higher death rates from ovarian cancer than those who never used ERT. Among former oestrogen users, the risk was 16 percent higher - a slight, but not significant increase. However, women who had used ERT for less than 10 years had no greater risk.
Postmenopausal oestrogen is already known to increase the risk of endometrial and breast cancer when used for a long time, but until this study, the effect of postmenopausal oestrogen use on ovarian cancer had not established.