There are certainly a lot of vegetarians and vegans in the world who consume no animal protein. However, there are also lots of vegetarians and vegans that get cancer. What I think the important point is here is that no diet, vegan or otherwise causes or cures cancer and that good or bad results involve a lot more than just whether you get cancer or not.
There are a few specific proteins and enzymes and vitamins that are only available from animal proteins and some vegans compensate for that with synthetic supplements. A person's diet is a long term way of eating, not something you do for a few weeks or months to lose a few pounds. In the grand scheme of things, animal protein in moderation or vegan is more a matter of preference than a matter of health.