So sorry to hear of the biopsy results, but delighted to hear that "Howie" seems to have a "new lease on life" with a change in his food. I switched my cats to Wellness as well, and altho they weren't sick, they do have more energy and are happier.
He certainly sounds like a much happier cat now, and hope the chemo treatments will be successful
and give him and you many more wonderful years together. Howie sounds like quite a character!