A 62-year-old man presents with a 3-month history of alternating diarrhea and constipation, decreasing stool caliber, and left lower abdominal cramping. Colonoscopy reveals a lesion in the sigmoid colon. The barium enema shows the appearance marked as **C** in the diagram — a narrowed lumen with heaped edges creating an apple-core deformity. Which of the following pathogenic mechanisms is MOST likely responsible for the development of this lesion?