I'm a biochemist with a biomedical background. Everything that follows is a simplification, but it's truthy. We understand pretty well what causes cancer in "o

I'm a biochemist with a biomedical background. Everything that follows is a simplification, but it's truthy. We understand pretty well what causes cancer in "otherwise healthy individuals" (eg.: assuming there aren't particularly bad genes involved... which is a whole thing on its own), it's not a big mystery. We know with total certainty that "cancer in general" is not usually caused by viruses, although some viruses are notorious for causing cancer. What causes cancer is whatever causes tissue injury and inflammation, with some probability. This is why smoking causes cancer, why drinking alcohol causes cancer, why sunburns cause cancer, why ionizing radiation causes cancer... The more chronic or frequent the injury/inflammation, the more the odds stack up against you. Viruses that cause chronic inflammation cause cancer. (There are also a bunch of things that directly cause mutations including some of the above, and those cause cancer too, with some probability, if they overwhelm error-correction mechanisms.)