A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 42-year-old man comes to the physician because of a 6-week history of intermittent fever, abdominal pain, bloody diarrhea, and sensation of incomplete rectal emptying. He also has had a 4.5-kg (10-lb) weight loss over the past 3 months. Abdominal examination shows diffuse tenderness. Colonoscopy shows circumferential erythematous lesions that extend without interruption from the anal verge to the cecum. A biopsy specimen taken from the rectum shows mucosal and submucosal inflammation with crypt abscesses. This patient is most likely at risk of developing colon cancer with which of the following characteristics?
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A
Unifocal lesionIncorrect. UC-associated CRC is typically MULTIFOCAL (often arising from multiple dysplastic foci), not unifocal as in sporadic CRC.
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B
Late p53 mutationIncorrect. In UC-associated CRC, p53 mutation is EARLY (often the first mutation), not late as in the adenoma-carcinoma sequence of sporadic colorectal cancer.
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C
Non-polypoid dysplasiaCorrect. UC-associated colon cancer arises from flat (non-polypoid) dysplasia rather than visible adenomatous polyps, complicating surveillance.
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D
Low-grade lesionIncorrect. UC-associated CRC tends to be HIGH-grade, not low-grade, and is often poorly differentiated compared with sporadic colorectal carcinoma.
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E
Right-sided predominanceIncorrect. sided predominance is characteristic of sporadic CRC arising from microsatellite instability (Lynch); UC-associated CRC is distributed throughout the inflamed colon rather than preferentially right-sided.
↑ Tap an answer to reveal the reasoning
Answer: C. Chronic bloody diarrhea, tenesmus (incomplete rectal emptying), weight loss, and a colonoscopy showing CONTINUOUS circumferential erythematous lesions from the anal verge to the cecum with crypt abscesses and mucosal/submucosal inflammation describe pancolitis-pattern ulcerative colitis. The continuous involvement without skip lesions and the rectal involvement are key distinguishing features from Crohn disease.
Colon cancer arising in the setting of long-standing ulcerative colitis differs from sporadic colorectal cancer in several important ways:
- More likely to be MULTIFOCAL (not unifocal)
- Arises from non-polypoid (flat) dysplasia rather than adenomatous polyps
- p53 mutation occurs EARLY (often the first mutation), unlike sporadic CRC where p53 is a late event
- More commonly HIGH-grade dysplasia and high-grade tumor
This means surveillance colonoscopy in UC focuses on biopsying flat mucosa for dysplasia rather than just removing visible polyps, and colectomy is recommended for high-grade dysplasia even without visible mass because of the flat dysplasia pattern.
**Why each option:**
**A.** UC-associated CRC is typically MULTIFOCAL (often arising from multiple dysplastic foci), not unifocal as in sporadic CRC.
**B.** In UC-associated CRC, p53 mutation is EARLY (often the first mutation), not late as in the adenoma-carcinoma sequence of sporadic colorectal cancer.
**C.** Correct. UC-associated colon cancer arises from flat (non-polypoid) dysplasia rather than visible adenomatous polyps, complicating surveillance.
**D.** UC-associated CRC tends to be HIGH-grade, not low-grade, and is often poorly differentiated compared with sporadic colorectal carcinoma.