How reliable is a ab CT scan for colon cancer? Had 3, what percentage of cancers are missed in a CT scan? Trying to find stats.

Colon cancer. A ct scan is not the diagnostic modality of choice to find colon cancer. It may find late cancers that are causing symptoms but if you want to find colon cancer or precancerous polyps you need a colonoscopy.
Not good. This same question has been asked several times today. A ct scan will not see a colon cancer unless it is large enough and advanced enough so that it could then be seen. Colonoscopy will see a colon cancer at a much earlier stage. I know of no statistics for what you are asking.