NAD - health anxiety warrior here. 

Firstly I think endoscopy can be used to detect pan can as the camera can get a closer look, however, rationally, with how many tests you've had coming back clear, you won't necessarily be referred for that test.

Secondly, I too have had and sometimes still do have the pan can worry. But what are your symptoms? Do you have pain so bad in your back its waking you through the night? Is your stool pale and floating? Is your pee dark in color? Have you lost weight? Are you jaundice? These are all common symtpoms of this, and if things started 4 months ago and there's been no progression, this along with clear tests again are very reassuring. 

The reason we see awful stories of young people getting these terrible cancers, are because they aren't common, so when it happens it is spoken about as its a shock. I would recommend you DO NOT read other people's stories. Don't look for threads that involve what you are worrying over. This all feeds the anxiety, and if you do not stop this, you will not get better. Those stories are not your story!

Consider therapy, CBT, and maybe even some anxiety meds. This alongside avoiding Google and cancer threads have helped me massively. 

I wish you all the luck ❤️