>>Vecr+(OP)
Usually, yes. But there do exist infectious cancers that spread between individuals. One is the face cancer that's been killing Tasmanian devils[0]... it started in one individual and spreads to others when they fight (biting each other). Apparently there's a similar (although rarer) cancers that's sexually transmitted between dogs.
[0] https://en.wikipedia.org/wiki/Devil_facial_tumour_disease