Right, but that's within a single host isn't it? Like patient A gets that mutation and succumbs, that sucks, but the stronger cancer cells don't them jump to patient B the way antibiotic-resistant bacteria do.
(barring the transmissible cancers article that your sibling comment linked to, but that's not the common case)
(barring the transmissible cancers article that your sibling comment linked to, but that's not the common case)