Dependence of the slope on the degree of heterogeneity in the number of required driver genes across tissues.

<p>(A) Regression line (red), for predicted cancer risk if it is assumed that all cancer types require exactly the same number of driver gene mutations, n, as assumed by Little et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0175535#pone.0175535.ref001" target="_blank">1</a>]. The slope of the regression line is 0.5. (B) Regression line (red), for predicted cancer risk if it is assumed that different cancer types require different numbers n of driver gene mutations (two in bone, ovarian, thyroid, gallbladder, brain, and lung cancer, and three drivers in all other cancer types.) To make the data points homogeneous in n, in order to regress on them, their risk was modified according to an Armitage and Doll model, for simplicity, with a mutation rate u = 5x10^-7 per gene per cell division. All other variables were identical to those in A. The slope of the regression line is 1.8.</p