What's the chance of an occult lung cancer causing 7 years of fatigue and other non specific issues but not showing on a ct scan of the chest. thought about paraneoplastic syndrome but these seem very rare & cancer normally appears within a few years?

If you have been a smoker they are not zero. But would expect that it would be showing up after 7 years. Your body is talking to you. Listen and take good notes and share with your Dr to help get to the bottom of what is going on.

A lung cancer causing symptoms would not remain occult for 7 years. It is more likely that there is an alternative explanation for your symptoms.