Just plain bad luck? Stem cell division rates play major role in cancer risk

Researchers have estimated that around 65 percent of variation in cancer rates between tissue types is related to the number of stem cell divisions, explaining why cancer occurs more commonly in some parts of the body than others.

The researchers, reporting in Science, used data from the scientific literature on stem cell division rates in 31 different tissue types. They then plotted the total number of stem cell divisions against the lifetime risk of cancer in each particular tissue type, revealing a strong correlation between the two.

'All cancers are caused by a combination of bad luck, the environment and heredity, and we've created a model that may help quantify how much of these three factors contribute to cancer development,' said study author Professor Bert Vogelstein from Johns Hopkins University School of Medicine.

'Cancer-free longevity in people exposed to cancer-causing agents, such as tobacco, is often attributed to their "good genes" but the truth is that most of them simply had good luck,' he added.

However, some commentators have criticised the 'bad luck / good luck' terminology used by the researchers and the media.

Writing on the Cancer Research UK Science Blog, Henry Scowcroft says: 'According to the researchers, the maths could explain two-thirds of the variation between different tissues.'

He continues: 'The media coverage has inadvertently jumped from talking about cancer rates in
different tissues to speculating about cancer rates in the population.'

Scowcroft also notes that the research only looked at tissue types for which solid data on stem cell divisions were available, leading to two notable exclusions - breast cancer and prostate cancer - and limiting what we can conclude from the findings.

Additionally, a feature on the NHS Choices website highlights that in the authors' statistical analyses, the 65 percent figure was not particularly robust, and the true estimate based on the researchers' data could lie anywhere between 39 and 81 percent.

In an updated press statement, Professor Vogelstein and co-author Dr Cristian Tomasetti defended their research findings against criticism that it suggests that people cannot protect themselves from cancer.

'This doesn't mean that cancer research should be stalled in any way. Quite the opposite - our research emphasizes the likelihood that more cancers will appear in the future simply because aging increases the number of stem cell divisions. Research on primary and secondary prevention, cancer treatment, and the biology of the disease is more important than ever.'