  Tomasetti and Vogelstein recently proposed that the majority of variation in
cancer risk among tissues is due to "bad luck," that is, random mutations
arising during DNA replication in normal noncancerous stem cells. They
generalize this finding to cancer overall, claiming that "the stochastic
effects of DNA replication appear to be the major contributor to cancer in
humans." We show that this conclusion results from a logical fallacy based on
ignoring the influence of population heterogeneity in correlations exhibited at
the level of the whole population. Because environmental and genetic factors
cannot explain the huge differences in cancer rates between different organs,
it is wrong to conclude that these factors play a minor role in cancer rates.
In contrast, we show that one can indeed measure huge differences in cancer
rates between different organs and, at the same time, observe a strong effect
of environmental and genetic factors in cancer rates.
