Cancer, Stem Cells, and Bad Luck

written by Ted Schettler, MD, MPH
Science Director

Ted SchettlerThe new year got off to a fast start in cancer-related research with a paper published in the January 2nd issue of the prestigious journal Science titled “Variation in cancer risk among tissues can be explained by the number of stem cell divisions”, co-authored by C. Tomasetti and B. Vogelstein of Johns Hopkins University.  The authors “show that the lifetime risk of cancers of many different types is strongly correlated (0.81) with the total number of divisions of the normal self-renewing cells [stem cells] maintaining that tissue’s homeostasis.”

They based this conclusion on a comparison of lifetime risk of cancer in various tissues (expressed logarithmically) with an estimate of total lifetime stem cell divisions in those tissues for which there is some agreement about stem cell mass and dynamics. Breast and prostate cancers were not included because of lack of consensus around stem cell properties.

The paper says they included 31 tissue types, but actually it was fewer since the authors double counted lung, liver, head and neck, duodenum, and colorectal, each of which they evaluated with and without known links to cancer (smoking, hepatitis C virus, human papillomavirus, and familial adenomatous polyposis, respectively). For the tissues evaluated, the correlation between lifetime cancer risk and total number of stem cell divisions was quite strong. And, by separating smokers from non-smokers, the analysis clearly shows that lifetime lung cancer risk is much higher in smokers, assuming a similar number of lung stem cell divisions in the two groups. So far so good.

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