My Husband Has Been Battling Stage Four Colon Cancer For

My husband has been battling stage four colon cancer for three years. We thought he was doing better. But during a cat scan they found a nodule that had grown to a centimeter in only six weeks had all the hallmark of dangerous nodule so they did a pet scan. And it didn't show up. What's going on even doctor is baffled. Is my husband sugar to high. To read correct pet scan