Hi and welcome to HCM,thank you for your query.
This is very good new that he survived so many years in stage 4. I dont thnik that white spot is related to colon cancer
but it should be evaluated by specialist and sent to patohistologic analysis. i am sure this is not malignant and he should only do frequent follow up with colonoscopise and pet ct scan
from time to time.
Wish you good health. Regards.