My grandmothers mom had colon cancer in her 70's. my grandmother is still alive and mom has no risks but should we be screened early because of this?

No: Screening for colon ca starts at age 50. If there is positive family history in first degree relatives - parents and siblings, then screening starts at age 40 or 10 yrs younger than the affected family member, which ever comes first. Since grand mothers mom is not considered a first degree relative, no reason to screen early.

Yes need screening: Screening colonoscopy starts at the age of 50 to 75 , with strong family history done earlier age. Simple routine screening tests like stool for occult blood , rectal exam , sigmoidoscopy should be done, if your mom is over 40 yrs advisable o have a screening colonoscopy.

Take a test: Because your grandmother had colon cancer, your mother is considered to be at risk and since i suspect she is in her 50's, she should have a screening colonoscopy. There are on-line risk assessment tools for risk for colon cancer - you might try the test located at the following url: http://digestive.Ccf.Org/.