Figure 8

A cartoon illustrating the central role of chance in cancer formation, based on the fact that somatic mutations are stochastic events. Inherited factors (see text and Fig. 6) can modulate the process, but they somatic mutations are still needed for the onset of cancer; and environmental factors work in large measure by increasing either the mutation rate (mutagenic agents) or the number of cell divisions (e.g. with an inflammatory process, such as one caused for instance by Helicobacter pylori).