[throwaway234287]

I'm not an expert, but my understanding is that the probability or rate (or expected time) of metastasizing varies a lot depending on the type of the tumor. (I looked into this a bit when I was diagnosed; it was more or less likely to metastasize within a somewhat short time, depending on the exact type of the tumor.)

I'm sure the immunosuppressants needed after a transplant would increase the risk in any case.