Roughly two-thirds of cancer types researchers recently studied largely appear to be the result of random mutations and not inherited genes or environmental and lifestyle factors. Reporting in the journal Science, researchers at the Johns Hopkins University School of Medicine investigated 31 common cancer types and found that 22 of them (including leukemia, bone, testicular, ovarian, and brain cancer) appear to mostly be attributed to just plain bad luck; the nine largely attributed to genes and lifestyle include skin, colorectal, and lung cancer. The analysis revolved around stem cells, which comprise a small number of the total cells in most tissues but tend to be where tumors form because they are constantly dividing to repair damaged tissue—and thus there is, simply mathematically, more opportunity for mutations to occur in these cells.
What was reviewed: the number of stem cells in 31 tissue types, the rate of stem-cell division there, and the risk that a person would develop a cancer in that tissue. The researchers found a "strong" correlation between the lifetime risk of many cancers and the total number of cell divisions in the tissue, suggesting "only a third of the variation in cancer risk among tissues is attributable to environmental factors or inherited predispositions," they write. As for the remainder of the risk, "It’s losing the lottery," researcher Dr. Bert Vogelstein tells Reuters. An outside researcher tells the Wall Street Journal that more research is required to understand why different stem cells divide at the varied rates they do, as those rates could still be driven by genes and the environment. Breast and prostate cancer weren't included in the study because researchers couldn't lock down their division rates. (Some scientists say we'll never cure cancer.)