If someone is concerned about an underlying colon cancer, the first doctor they need to see is a gastroenterologist who will do a colonoscopy for them and see if there's any evidence of any abnormal lesions. Who should be screened for colon cancer? Everyone over the age of 50 needs one screening colonoscopy at age 50 and every 5-10 years thereafter. If there's a family history, then I would definitely recommend doing a colonoscopy before the age of 50. The exact age is not clear, but it's up to the patient and the family. Lately we have noticed an increased incidence of colon cancer in patients under 50 years of age, and if someone is having any symptoms of weight loss or abdominal pain, cramping, nausea, or rectal bleeding, then for sure they should go for a screening colonoscopy.