London: In what may spark a fierce debate, researchers claim that hormone replacement therapy doesn`t raise a woman`s risk of developing breast cancer.
A previous research, titled the Million Women Study, suggested that women taking hormone replacement therapy (HRT) were twice as likely to develop breast cancer and more likely to die from it than those not taking the therapy.
But, an international team, led by Prof Samuel Shapiro from the University of Cape Town, now says the Million Women Study, carried out by Oxford University, is "fundamentally flawed", `The Daily Telegraph` reported.
According to the researchers, there were many flaws in the Million Women Study, including that women may have already had breast cancer when they were enrolled in the research, and that they were at increased risk of dying within three years which was "biologically implausible".
"The name `Million Women Study` implies an authority beyond criticism or refutation. Here we conclude that the evidence in the Million Women Study was indeed unreliable.
There were defects in the study design, and the findings did not adequately satisfy the principles of causation.
"HRT may or may not increase the risk of breast cancer but the Million Women Study did not establish that it does," Prof Shapiro wrote in the `Journal of Family Planning and Reproductive Health Care`.
The team also says inviting women to join the study would in itself have increased the number already aware of breast lumps or precancerous changes, leading to higher numbers of cancers being detected. Moreover, crucial data was missing.
"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.
"The Million Women Study was an observational study, and it has the attendant problems and uncertainties intrinsic to such studies. If the evidence was unreliable, the only effect of its massive size would have been to confer spurious statistical authority to doubtful findings," Shapiro wrote.
However, the authors of the Million Women Study refuted the latest claims. In a statement, Professor Valerie Beral and Professor Richard Peto at Oxford University said: "HRT is one of the most important causes of breast cancer in the world and women can easily change their risk by stopping."