A 54-year-old woman presents to the emergency department with bright red blood per rectum. She has had 3 large, bloody stools over the past 2 days, associated with mild abdominal cramps. She denies melena, fever, vomiting, or weight changes. She underwent a radical hysterectomy and adjuvant radiation therapy for cervical cancer 12 months ago. The patient has no other medical conditions and takes no medications. Vitals are normal: temperature 37.5°C (99.5°F), blood pressure 140/80 mm Hg, pulse 80/min, and respirations 12/min. Physical exam reveals a nontender and nondistended abdomen, with well-perfused extremities. Lab results show hemoglobin 9.8 g/dL, platelets 325,000/mm³, and leukocytes 6,200/mm³. Colonoscopy reveals mucosal pallor, friability, and multiple telangiectasias within the rectum, with scattered diverticula in the descending and transverse colon.