How high would chances be that symptomatic colon or rectal cancer be missed on 3 separate CT scans? Would this be very likely?

Possible to miss. The colon has many folds and turns with stool inside it. It would have to be big enough for a ct scan to show it and contrast inside the colon might help identify it on a ct scan. But it can miss a lesion. The best way to see colon cancer is taking a prep to clean out the colon and getting an endoscopy (colonoscopy) that can visualize the cancer and biopsy it at the same time.
Colo-Rectal Cancer . It wasn't clear to me whether or not you are "symptomatic." if not, and you are young colon cancer is more likely to appear after age 50 unless you have a cancer gene)> chances of missing a tumor on 3 ct scans are low, but possible. A better screening test is a colonoscopy. You should discuss this with your doctor if it remains a concern.

Related Questions

Could three CT scans over one year all really miss symptomatic colon cancer (narrow stools, blood). Problems for past 2 years, doc says no way it wou?

Yes. Colonoscopy is not the ideal way to evaluate for colon cancer. The most accurate test is a colonoscopy. Contact a gastroenterologist to set this up. Read more...
Absolutely. Ct scan is by no means designed for detecting colon cancer. When it does, it is most often in the advanced stages since it is large enough to have either formed metastatic diseases (e.g. In the liver) or distorted the anatomy of the colon enough to become evident. The most sensitive test for colon cancer is colonoscopy. Ct is not a good test for screening for colon cancer. Read more...