Exterior cancer

My 75 yo father has an unknown primary cancer diagnosis. Doctors are under the impression that it is stomach cancer and it is on the exterior portion of the stomach. His endo biopsy did not pick any thing up. He has bone mets. Nothing on scans for stomach cancer.

I would like to know is there any other way to diagnose/prevent this earlier in myself? I have several family members who passed from stomach cancer and was only caught at late stages. My dad went to his dr quarterly for a long time but was diagnosed pretty late.

My dad did not test positive for any genetics.