Confusion as Experts Raise Doubts over HRT Cancer Risk; ANALYSIS HIGHLIGHTS 'DESIGN FLAWS' IN ORIGINAL STUDY
Byline: MADELEINE BRINDLEY
WOMEN face further confusion about the safety of HRT after a group of experts questioned the link between the therapy and breast cancer.
A link between hormone replacement therapy for menopausal women and the disease has proved controversial, with several studies suggesting the finding has been blown out of proportion.
But other research has reinforced the link or shown a drop in breast cancer rates alongside declining HRT use.
In a paper published in the Journal of Family Planning and Reproductive Health Care last night, experts from South Africa, Germany and the UK said the Million Women Study - which has reiterated the link several times - does not establish HRT as a cause of breast cancer.
But they have not ruled out that HRT may increase the risk of the disease.
First published in 2003 and funded by Cancer Research UK, the Million Women Study found that using combined HRT doubles a woman's risk of de-veloping breast cancer compared with women not taking HRT.
An update last August found similar results after a longer follow-up, including a "rapid fall in risk after HRT is stopped".
But the new paper, analysing the study concluded: "HRT may or may not increase the risk of breast cancer, but the Million Women Study did not establish that it does."
The authors examined criteria applied to scientific research to show a causal link, such as biases and biological implausibility, to review the findings of the study.
Their analysis highlighted design flaws that they say would have skewed the findings. For example, cancers detected within a few months of the study's start would have been present when the women were enrolled in the research, but these were not excluded, they said.
Inviting women to join the study would have increased the number already aware of breast lumps or pre-cancerous changes, leading to higher numbers of cancers being detected (detection bias), they added.
They said: "The name Million Women Study implies an authority beyond criticism or refutation.
Many commentators, and the investigators, have repeatedly stressed that it was the largest study of HRT and breast cancer ever conducted.
"Yet the validity of any study is dependent on the quality of its design, execution, analysis and interpretation. …