This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Inflammatory bowel disease, Subject name: Surgery
Risk of carcinoma in ulcerative colitis: 
Select and explain. 
A. 20% after 20 years, B. 35% after 30 years, C. 30% after 30 years, D. 50% after 30 years
B: 35% after 30 years
Answer: B: 35% after 30 years 
Explanation: Cumulative risk of cancer increases with duration of ulcerative colitis, reaching 25% at 25 years, 35% at 30 years, 45% at 35 years and 65% at 40 years The risk of malignancy in Crohn's pancolitis is similar to UC pancolitis, i.e. 2% after 10 years, 8% after 20 years and 18% after 30 years approximately.