He had no tumor. He had a clot, and since these types of clots sometimes are an early warning of a specific type of cancer down the road, they biopsied around that area and found a cell or two. They're zapping it just in case.
He's going to have years to live, cancer-free because they nipped this in the bud long before it even began to form a tumor.
We're stuck with him for at least the remaining 3 years of his current term, and possibly for another one after that.