Challenge to HRT-breast cancer link
Tuesday January 17th, 2012
A new challenge is made today to a landmark British study which helped discredit the use of hormone replacement therapy by women.
A group of international experts claims the Million Women study, which linked HRT to breast cancer, was flawed.
Writing in the Journal of Family Planning and Reproductive Health Care, the researchers claim the analysis was flawed.
The British-based study was run in parallel with major research elsewhere, such as the US-based Womens Health Initiative.
Its findings on HRT and breast cancer were reported in 2004. It also found link with endometrial and ovarian cancer.
The research suggested that the combined oestrogen-progestagen treatment doubled breast cancer risk. The latest findings were published last August.
But now Professor Samuel Shapiro, of the University of Cape Town Medical School, South Africa, and four other experts from the UK, Australia and Germany claims the research is flawed - mainly because it used women undergoing breast screening.
The experts all admit they have acted as consultants to HRT manufacturers - and mostly still do.
Professor Shapiro says the rates of breast cancer among all the women studied - including those not on HRT - were higher than normal as a result. And, he suggests, this is partly because women worried by existing lumps are more likely to agree to undergo breast screening.
He states: "Breast cancer can sometimes grow slowly, and remain undetected for years. Even a small bias resulting in the detection of one to 1.2 extra cases each year among 1000 women who had used HRT for five years, or an extra 1.5 to 1.9 cases in those using HRT for 10 years, would have invalidated the overall findings."
He adds: "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. Size alone does not guarantee that the findings are reliable."
* In their report last August the original study's authors said there was a clear pattern of risk following the adoption of HRT - with risk levels returning to normal when women gave up the treatment.
The Journal of Family Planning and Reproductive Health Care January 17 2012 doi: 10.1136/jfprhc-2011-100229
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