Study finds HRT may not cause breast cancer

17 January 2012

Women undergoing hormone replacement therapy (HRT) may not be at increased risk of breast cancer, according to a new study that questions previous research suggesting a causal link between the two.

Published in the British Medical Journal's Journal of Family Planning and Reproductive Care, the research from the Million Women Study (MWS) showed that HRT may not be a causing factor for the development of the disease in women going through the menopause.

The authors of the current MWS looked at the general causal criteria applied to the previous four reports from 2003, 2004, 2006 and 2011 and applied the notion of biases and biological implausibility to see if they could have affected the original findings.

"If the evidence was unreliable, the only effect of its massive size would have been to confer spurious statistical authority to doubtful findings," the researchers wrote in the study.

Some of the women tested were examined just a few weeks after beginning the HRT and could have already had unknown cancer growth previous to the treatment, they suggested.

Furthermore, the researchers allotted some of the cases to the fact that breast cancer can sometimes grow slowly and remain undetected for years.

HRT replaces the female hormone oestrogen in women who have stopped releasing eggs. The lack of the hormone can cause hot flushes, vaginal dryness and a loss of sex drive.

Posted by Jeanette Royston

"Does hormone replacement therapy cause breast cancer? An application of causal principles to three studies Part 4", The Million Women Study Online First 2012

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