For some reason, none of the abdominal cancers seem to have a good prognosis, except for colon cancer, and that's only if you catch it early. I don't know why that is.
Any kind of stomach cancer is bad news -- not just the metastatic variety. That's usually late stage, anyway. Maybe the abdominal cancers are hard to treat because they cause so few distinctive symptoms in the early stages.
If I had a family history of stomach cancer, you can bet I'd have myself checked out pretty frequently, and I'd definitely tell my doctor I had a family history of it. Sometimes, mentioning little details like that can make all the difference in your prognosis.