It is true that having multiple 1st and/or 2nd degree relatives with colorectal cancer also increases your risk of this disease. At the same time, rectal bleeding is rather common in people with constipation, and so rectal bleeding, alone, does not mean that you have colorectal cancer. Given your family history, though, it is important that you undergo colonoscopy. Additionally, it might also be appropriate for you to see a genetic counselor after your colonoscopy, to further discuss your family history of colorectal cancer.
Sincerely/ Robert A. Wascher, MD, FACS
www.doctorwascher.com
www.oncoguard.com