Cancer over and over again

My Grandfather died of lung cancer. My Father died of colon cancer. My Father in Law died of liver cancer less than 6 months ago. My Mother was diagnosed with ovarian cancer a week before Thanksgiving. She is undergoing chemo and suffering from the side effects as I write this. It is very difficult to see so many wonderful people suffer the same fate. So many of the symptoms and weakness of body seem to repeat themselves only causing the memory of each of the loved ones who have passed to come back so clearly. I feel like a veteran of this disease in the caretaking aspect, but it is really taking its toll. Not sure where to turn. Any advise in keeping a positive outlook in the face of a terminal illness? I feel as if I wish I hadn't seen this all before so I wouldn't know what was coming.