Findings from observational studies have suggested that long-duration HRT use is associated with an increased ovarian cancer risk but HRT and regulatory guidance vary in what is said about ovarian cancer risk. The Women's Health Initiative trial, which confirmed an increased breast cancer and cardiovascular risk, was not powered to evaluate rare endpoints such as ovarian cancer. Furthermore, the trial was mainly designed to assess short-term use and short-term health effects.
The current findings support the addition of ovarian cancer as an adverse effect of HRT. The study authors note that the findings that ovarian cancer risk is greatest in current users of hormone therapy, falls after use ceases, and varies by tumour type, suggesting that the increased risk may be causal. If it is, they add, “women who use HRT for 5 years from around age 50 years have about one extra ovarian cancer per 1000 users and, if its prognosis is typical, about one extra ovarian cancer death per 1700 users.”
An editorial notes that given the limitations of the current observational data, it is still not clear whether the current recommendation to use hormone therapy for the shortest duration possible is appropriate for women who are concerned about an increased risk of ovarian cancer.
In response to these findings, the MHRA advises that the lowest effective dose of HRT should be used for the shortest possible time. They propose to evaluate these findings and their implications for shorter-term use with updates to product information as necessary.