In order for a cancer-like mutation to kill a plant it would probably have to cause mechanical damage. Tumors completely circling the trunk of a tree might have

In order for a cancer-like mutation to kill a plant it would probably have to cause mechanical damage. Tumors completely circling the trunk of a tree might have an effect like girdling the tree and kill the tree. A tumor growing in the center of a stem might compress the xylem and phloem enough to choke them off. This kind of fatality happens with humans, too, even if the cancer doesn't spread beyond the origin site.