Cancer: Scientists split over role of lifestyle in causing disease

It is the clash of the scientific titans. The question at issue: to what degree is developing cancer simply down to bad luck, rather than the toxic effect of our genes and our lifestyle or environment?

That smoking is a cause of lung cancer is an established fact. But to what extent can cancer generally be avoided? On that, scientists are divided.

In the red corner, a mathematician and a cancer researcher from John Hopkins University in Baltimore, Maryland, who claimed in the journal Science earlier this year that as many as two-thirds of all cancers were down to luck rather than factors such as smoking.

In the blue corner, two cancer researchers from Stonybrook University in New York who have this week responded in the journal Nature claiming the reverse – at least two- thirds of cancers (and possibly up to 90 per cent) are caused by environmental exposure to carcinogens – and are therefore potentially avoidable.

Who is right? Whatever the answer, this is a vital battle. What is the point in spending millions persuading the public to adopt healthier lifestyles if we can avoid only 10 per cent of cancers that way? It would be better to put the cash towards earlier detection.

Cancer occurs when stem cells in the body go suddenly rogue and divide out of control, creating cancerous growths. This may be determined internally, by the way cells operate, or externally by factors such as tobacco smoke, sunlight and infections.

Cristian Tomasetti and Bert Vogelstein, from John Hopkins University, argued in Science that while there are some obvious extrinsic factors that cause cancer, such as tobacco smoke, the key determinant was the number of times the cells in a particular tissue divide. The more divisions, the greater the chance of a mutation occurring. But this is beyond our control, so we should stop worrying about preventing it and focus on detecting it.

Back came Yusuf Hannun and his team from Stonybrook University this week, who argued in Nature that mutations during cell division rarely build up to produce cancer, even in tissues with high rates of cell division. Exposure to an environmental carcinogen, such as cigarettes or sunlight, is almost always required.

Dr Hunnan notes that cancer incidence varies around the world. Breast cancer is five times higher in western Europe than in eastern Asia, and prostate cancer 25 times higher in Australia and New Zealand – the highest rate in the world – than south-central Asia. Yet people who migrate from Asia acquire the higher risk of the new country.

No single risk factor has been identified for breast and prostate cancer, suggesting their causes are complex. But for others the picture is clearer, they say. For colorectal cancer, 75 per cent of the risk is attributable to diet, and around 90 per cent cervical cancer is attributable to infection with human papilloma virus, preventable by vaccination.

The flaw in the earlier paper, Dr Hannun said, was that it considered internal and external factors as independent. Yet we know radiation causes cancer, and it does so by affecting internal stem cell division rates.

Overall, 70 to 90 per cent of cancer is preventable, he said. But that depends on knowing what to avoid and, importantly, having the will to avoid it.