Probably the last thing you need right now is a story, but I am going to tell this one anyway.
We have a friend of the family whose neighbor was diagnosed with liver cancer. When they took a scan they could actually see two spots, which were the cancer. After treatment with chemotherapy (which was very rough,) they did another scan and the neighbor said the spots were no longer visible. It is amazing what they can do to treat cancer now.
May God guide your grandfather's doctors, so they will know how to treat him effectively and may God give your grandfather the strength to deal with the treatments. Your grandfather is lucky to have you and the rest of your family to help him and support him during this time.