Further doubts cast on study linking HRT with breast cancer

A link between HRT and the disease has proved controversial, with several studies suggesting the findings were blown out of proportion.

However, other research has reinforced the link or shown a drop in breast cancer rates alongside declining HRT use.

Experts writing today in the Journal of Family Planning and Reproductive Health Care said the Million Women Study in the UK – which has reiterated the link several times – does not in fact establish HRT as a cause of breast cancer. However, they did not rule out that HRT may increase risk of the disease.

First published in 2003 and funded by Cancer Research UK, the Million Women Study reported that using combined HRT doubles a woman’s risk of developing breast cancer compared with women not taking HRT.

An update in August last year found similar results after a longer follow-up, including a “rapid fall in risk after HRT is stopped”. But today’s experts insisted: “HRT may or may not increase the risk of breast cancer, but the Million Women Study did not establish that it does.”

The authors highlighted several design flaws that would have skewed the findings. For example, cancers detected within a few months of the study’s start would have already been present when the women were enrolled in the research, but these were not excluded.