Can plants get cancer? Well, let’s first define cancer: In this case, cancer is the uncontrolled division of abnormal cells. And in plants, that can happen—sort of.
Trees do get cancer, but the tumors can’t metastasize because the cells are enclosed by rigid cell walls, which means they can’t migrate to other areas of the tree. So even when cells begin to proliferate uncontrollably, they usually don't do too much damage—the result is often those knots in trees called galls or burls.
Watch Hank Green from SciShow explain in further detail: