There seems to be a connection between thymoma and myasthenia gravis, but it's hard to tell from the literature which comes first (chicken and egg syndrome, also known as cart-before-the-horse disease). But that may be what Wilson's real concern is -- that he'll develop MG, or he's already showing symptoms that he thinks are related to MG. If he does have both, the prognosis is not as good as for thymoma alone,

MG is an auto-immune disease; for some auto-immune diseases, e.g. celiac, the incidence of lymphoma is higher than that for the general population. (The faster the immune cells proliferate, the more likely a cancer-causing mutation will arise.) /pedantic