Plants have an exclusive cancer prevention in the rigidity of their bodys. The solid cellwalls and hydrostatic pressure prevent a lot of deseases from moving inside of them. Cancer too is inhibited by this, and is forced to grow localy. As you might guess, that isnt exactly possible for use in animals.

Plants can in fact develop cancer. The bulbous growths near the ground are often exactly that. They can among other things be caused by the bacterium agrobacterium tumefaciens. We use them for genetic editing of plants.

When we want to grow a lot of similar plants, like orchids for example, we start with a single cell and, with different hormons, go from meristemic cultures to callus cultures. Those are basically cancerballs.