Abdominal cat scan show colon cancer?

Maybe yes..: If the cancer is very early--tiny and has not spread to local lymphnodes etc...It may not. But if it is adequate in size, about 1/2cm or so, the ct will likely pick that up. Ct scan has really good resolution these days and with the trained eyes of the radiologists, I am sure you will be given a thorough reading/evaluation. Consult your doc.. Good luck.

Sometimes: Usually colonoscopy with biopsy is the best way to make that diagnosis. Screening colonography (a ct based test) can identify larger masses in the colon, but standard colonoscopy would still be required for diagnosis.

Unreliable: Specialized cts that are designed to identify colon cancers (ct colonography) are available, but require a specific bowel prep and regimen to be effective. Routine ct scans will miss many small colon cancers that colonoscopy will find--colonoscopy remains the gold-standard.