Hi and welcome to HCM,thank you for your query.
It can be refered pain from lung cancer
since it can irritate pleura
and intercostal nerves. also it can be sign of stomach issue or back issue. he should see pain specialist to find the most appropriate medication therapy for him. Also,he should do frequent check up to rule out cancer recurence.If pain persists he should do spine mri
and check stomach and pancreas
Wish you good health. Regards.