Tuesday, September 27, 2005

A one-sided risk

'Breast cancer more likely in left-handers' reports the Daily Telegraph, among many others. A Dutch study published in the British Medical Journal found that left-handed women were 39 per cent more likely to develop breast cancer compared with right-handed women. The link was even stronger among women who developed breast cancer before the menopause. The researchers have suggested that the additional cancer risk may be caused by exposure in the womb to the hormone that is thought to cause left-handedness.

The rather bizarre conclusion of this study has been widely reported - but the evidence for any such link is very thin.

While the researchers started out recruiting over 12,000 women to their study, the follow-up required was beyond their resources, so a random sample of around 1,500 was used, of whom only 165 were left-handed. Given such small numbers, the risk of this being a freak result must have been quite high. In particular, the extra risk seemed to disappear in women who were not parents or were overweight, and it fell considerably in older women. If left-handedness were a significant cancer risk, it is strange that it should not apply to these groups.

As Emma Taggart of Breakthrough Breast Cancer told the BBC: 'Women who are left-handed should not worry about these findings. Although this is an intriguing study, it doesn't give us enough evidence to link left-handedness with breast cancer.' The strongest risk factor for breast cancer - in fact, pretty much any form of cancer - remains age. Eighty per cent of breast cancer cases are in the over-50s.

What the coverage of this report illustrates is that cancer has taken centre stage in our hyperchondriac age. The causes of cancer are not well-known and lend themselves to a great deal of speculation. While this study seems implausible, many other equally implausible links - passive smoking, sunbathing, pesticide residues - have been taken more seriously, with negative consequences for public discussion about how we socialise, what we eat, and many other activities.

In reality, apart from not smoking, there's very little we can do about cancer except to improve the treatment of it. But the obsession with avoiding cancer has led to an epidemic of unnecessary anxiety.