Gastrointestinal Oncology and Hereditary Syndromes
Core concepts
Know screening and hereditary syndromes. Colorectal cancer screening begins at age 45 in average-risk adults; colonoscopy every 10 years, or stool-based testing annually or every 3 years. Lynch syndrome (mismatch repair deficiency) features right-sided colon cancer, early age, and extracolonic cancers; test tumors with immunohistochemistry or microsatellite instability. Familial adenomatous polyposis requires colectomy due to near-certain cancer risk. Hereditary diffuse gastric cancer (CDH1) may warrant prophylactic gastrectomy.
Esophageal adenocarcinoma arises from Barrett; squamous cell carcinoma links to smoking and alcohol. Gastric cancer risk factors include H pylori, atrophic gastritis, and pernicious anemia. Pancreatic cancer presents with painless jaundice and weight loss; CA 19-9 is a marker, not a screening test. Hepatocellular carcinoma surveillance uses ultrasound with or without alpha-fetoprotein every 6 months in cirrhosis.
Traps
Do not use tumor markers for screening. Distinguish surveillance intervals by risk. Questions test that Lynch syndrome screening applies to all colorectal cancers, not just young patients. Do not confuse FAP with attenuated polyposis.
Rule of thumb
Any colorectal cancer diagnosed before age 50, or with mismatch repair deficiency on any tumor, should prompt genetic evaluation for Lynch syndrome.