Complicated question, and very loooonng. Please see below. Thanks.?

My grandpa has had his stomach tumor surgery for quite sometime now. Around 3 years I think. After his 6th chemotherapy session he has had a normal CA199. Half a year later he went to the hospital to do a complete body check, and found out that he has a CA199>500. The doctor suggested 2 more sessions of chemotherapy, which he did. After that he still has a CA199>500. He'd done all sorts of tests and scans and he has no problem. Recently he began to feel descomfort in the gastric area after meals. He went back to his doctor and after a series of tests and scans, he had no problem. Since the DOCTOR is NO help, I wonder if anyone here could please answer me what is wrong with my grandpa?