Figure 1.

Continued persistent infection by a pathogen (outer circle) requires host-cell survival (red), host-cell proliferation (yellow), and evasion of the immune system by the pathogen (blue). These pathogen-driven processes are achieved via various mechanisms that interfere with normal cell physiology and are outlined in Figure 2. Alterations in these normally highly regulated pathways can lead to transforming events that have been described as the 'hallmarks of cancer' (inner circle) [2]. Accumulation of such events can lead to cancer development. Cancer is not, however, an outcome that has been specifically selected by evolution to aid pathogen survival. Rather, it is more likely an unfortunate coincidence of pathogen capabilities selected to enable successful infection. Therefore, certain infections may not necessarily cause the infected individual to develop cancer, but may be an associated risk factor (Figure adapted from [2]).