The researchers, from the Johns Hopkins University School of Medicine in Baltimore, analyzed published scientific papers to identify the number of stem cells, and the rate of stem-cell division, among 31 tissue types, though not for breast and prostate tissue, which they excluded from the analysis. Then they compared the total number of lifetime stem-cell divisions in each tissue against a person’s lifetime risk of developing cancer in that tissue in the U.S.

The correlation between these parameters suggests that two-thirds of the difference in cancer risk among various tissue types can be blamed on random, or “stochastic,” mutations in DNA occurring during stem-cell division, and only one-third on hereditary or environmental factors like smoking, the researchers conclude. “Thus, the stochastic effects of DNA replication appear to be the major contributor to cancer in humans,” they wrote.

via Besides Lifestyle and Inherited Genes, Cancer Risk Also Tied to Bad Luck – WSJ.