How often does an upper endoscopy with biopsy miss cancer or pre-cancer in esophagus and stomach ? i have had one that said i had reflux esophagitis but thats it, but i am worried they missed something. how reassuring is this result?

No test is 100% sensitive even with biopsy; however, you should be reassured & not worried because your doctor already did what needs to be done. If you have reflux esophagitis, your symptoms will improve quickly with treatment (antireflux measures + diet + medication). If symptoms get worse even with appropriate treatment then both you and GI doctor will know repeat EGD is necessary. Good luck.