Why are colonoscopy performed years apart? shouldn't they be more often? doesn't cancer grow fast?

Guidelines: There are risks and benefits as well as costs associated with every medical procedure. That is why doctors have guidelines that have been established to help us monitor and screen for diseases like cancer appropriately. Patients who have risk factors (family history, inflammatory bowel disease, polyps, etc.) are screened more frequently.

Cancer slow growth: Cancer grows slow and steady. Colonoscopy and studies to look for cancer are done at a rate to still find cancer early but not too frequent. If you have a positive finding like a growth then your doctor will scope often, yearly or more frequently. This is true even for melanoma and all cancers. Remember all tests have risks.

Good question: Most colon cancer differs from other cancers in that it tends to progress in a very predictable pattern beginning as polyps that can sometimes form cancer. This process takes many years. For example, it can take 5 or more years for a polyp to reach 1 cm and then another 5 or more yrs for the 1 cm polyp to become cancer. This is why the standard recommendation is to have a colonoscopy every 10 yrs.