I googled “cancer that doesn’t show up on PET scan” and the first result was a certain type of stomach cancer.I currently have a friend who is in chemo for liver cancer and "unspecified/unknown" cancer. They know the liver cancer is met. from somewhere else but can't find it, it doesn't light up on the PET scans, etc. They THINK it's from chest or head area. I was just wondering if anyone knows how common it is for cancer not to show on PET scans but you actually have it. It doesn't look good for my friend right now.