I'm having some symptoms of colon cancer. how far has it progressed when you start having symptoms? does it vary?

May be none: There can be no symptoms at all all the way to bleeding, blockage, perforation, unwanted or unexplained weight loss. Symptoms may not be specific for colon ca. See your doc. You rsported a clean ct scan-that's good. What about the colonoscopy results? That's how the diagnosis would get made-biopsy of a tissue sample.

With advanced tumor: Colon cancer is relatively asymptomatic in early stages of development. As the lesion advances to the more advanced form even before metastasis, the tumor will bleed, perforate or obstruct the lumen of the bowel. The advantage of periodic colonoscopy is not so much to remove polyps accounting for about 10% of malignancies but to detect the onset of the malignant lesion prior to symptoms.