Genetic Testing in Hereditary Colorectal Cancer

CASE PRESENTATION  A 29-year-old woman presented to her family physician with a 2-month history of 30 to 44 mL (2-3 tbsp) of bright red blood per rectum with every bowel movement. She was referred to a surgeon, who performed anoscopy and gave her a diagnosis of hemorrhoidal bleeding. She underwent hemorrhoidal surgery of unknown type.The patient again sought medical attention 3 months later, complaining of persistent and unchanged rectal bleeding. She had no change in bowel habits, weight loss, or family history of colorectal cancer or polyps. Examination of her skin did not show osteomas, lipomas, or epidermoid cysts. Direct ophthalmoscopic examination revealed no pigmentation of the retinal epithelium. Abdominal examination was normal. A stool sample taken during rectal examination tested guaiac positive.The results of an upper gastrointestinal tract barium series were normal, but air contrast barium enema showed multiple filling defects throughout the colorectum. Subsequent colonoscopy revealed