Stem cells, environment, and cancer risk
Understanding the causes of cancer is one key part of the battle against this devastating disease. Environmental and genetic factors are commonly used to explain who gets cancer and in which tissues it develops. A study by Tomasetti and Vogelstein in January this year put forth a third factor—the total number of stem cell divisions in a given tissue—which they believe accounts for the majority of cancer risk (1). The underlying concept is that oncogenic changes to DNA can occur randomly, rather than as a result of environmental factors, and a greater number of cell divisions increase the risk of error. Plotting the lifetime risk of cancer in a particular tissue type against the total number of stem cell divisions in that tissue during the average lifetime of a human, they found a correlation of 0.81, and this correlation extended across five orders of magnitude. This led some in the general public to conclude that cancer is due merely to “bad luck”. The study identified cancers that are deterministic (influenced by an environmental component) or replicative (due mainly to random errors and representing the majority of cancers). While deterministic tumors can be prevented by vaccines and lifestyle choices, replicative tumors are best combated through secondary measures such as early detection.