What is the likelyhood of getting cancer if your one grandparent had died in 40s with colon cancer?

General population: If grand parent colon cancer is not genetically related cancer of colon, then incidence will be same as general population.

Unknown: The health history of all of your relatives would be helpful. You should be seen by your doctor and should probably have a colonoscopy before the recommended age of 50 due to your family history. If, after obtaining your family history, you may be recommended to be tested for a hereditary predisposition to colon and other cancers.

Low: While there are a number of genetic syndromes that involve colon cancers, they typically involve 2 or more family members before there is meaningful concern for a genetic syndrome. These can be investigated by blood tests.