Colorectal polyps Quiz: Ace Your Exams

A 39-year-old woman comes to her physician for evaluation of excessive fatigue and weight loss over the past 3 months. Menses occur every 28 days without heavy flow or severe pain. The patient’s mother died of endometrial cancer at the age of 48. Vital signs in the office include temperature of 37.0°C (98.6°F), pulse of 98/min, respirations of 14/min, and blood pressure of 125/85 mmHg. Physical examination reveals conjunctival pallor. Rectal examination is notable for guaiac-positive brown stool. Hemoglobin concentration is 10.2 g/dL, and mean corpuscular volume is 74 μm3. Colonoscopy shows a mass in the ascending colon. Pathologic examination of the resected mass reveals adenocarcinoma, and further genetic testing reveals a mutation in the MLH1 gene. This patient’s cancer is most likely due to a primary defect in which of the following cellular processes?