Quote Originally Posted by NichG View Post
While this story is primarily about genetic mutation, anything that disrupts the body's control over the replicative dynamics of its cells could be termed a cancer. That might mean that in some cancers its might not be specific genetic mutations causing the cells to break free but instead is some epi-genetic stuff like patterns of methylation, or something else in the surrounding context that drives those cells to grow uncontrolled, or other such things. In some cases there are viruses which modify cells to be closer to that break-free point, so those cancers are actually sort-of transmissible (in the sense that the thing provoking the cancer to become more likely is transmissible). I don't know of anything like this in humans, but in some animals there are cancers where the cancerous cells can directly infect another animal of the same species and can grow outside of their host (tasmanian devils have a cancer like this). So 'cancer' comprises a pretty diverse set of dysfunctions.
Viruses causing cancer is very interesting and often overlooked. I would just add there are environmental sources of genetic mutation that can also lead to cancer. Things like ionizing radiation, aromatic hydrocarbons, certain wavelengths of UV light, etc.