Until 2002 when HRT use dropped dramatically following the results of the Women's Health Initiative Trial (USA) that showed an increased risk of breast cancer in women taking HRT, Dr Renehan said that HRT masked and diluted the effects of obesity on the incidence of breast cancer. "In women who used HRT it wasn't clear what proportions of breast cancers were caused by HRT or by obesity. In women who don't take HRT, the effect of obesity was much clearer. Now that far fewer women are using HRT, it is much easier to see the effect of obesity on the incidence of breast cancer, and also on endometrial cancer. Consequently, the proportions of these cancers attributable to obesity have increased."

Dr Renehan said that although European countries were taking steps to tackle the obesity epidemic, this study underlined the urgency of the task and the scale of the problems caused by increasingly overweight populations.

"The overall size of the burden of increasing cancer incidence should inform health policy. For example, it is clear that, in both relative and absolute terms, obesity-related cancer is a greater problem for women than for men. At a country level, it is a greater problem for central European countries like the Czech Republic, whereas it is less of a problem in France and Denmark. Similarly, obesity-related oesophageal cancer seems to be a substantial and unique problem in the UK.

"The study also identifies priorities for research into certain cancers, namely endometrial, breast and colorectal cancers. In the face of an unabating obesity epidemic, and apparent failure of public health policies to control weight gain, there is a need to look at alternative strategies, including pharmacological approaches."

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