How soon can my cat have surgery to remove a tumor in his abdomen after his I131 treatment? They did an ultrasound and fine needle biopsy before the I131 treatment, and just before giving him the radioiodine, the vet told me that because he had a fever, he now thinks the tumor may be cancer--not benign, like he'd told me a couple weeks ago. So I want to have it removed asap, but don't know when that would be. I would have a local vet do the surgery--not the one who did the I131.