Right Colon Polypoidal Adenocarcinoma MCQ — NEET PG Practice Question | NEETPGAI
Right Colon Polypoidal Adenocarcinoma
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A 68-year-old postmenopausal woman presents with a 4-month history of progressive fatigue, dyspnea on exertion, and pallor. Laboratory investigations reveal hemoglobin 7.8 g/dL with microcytic indices and serum iron studies consistent with iron-deficiency anemia. Colonoscopy reveals the structure marked **A** in the diagram—a polypoidal fungating mass in the cecum with an ulcerated, friable, contact-bleeding surface. Biopsy confirms adenocarcinoma. Which of the following BEST explains why right-sided polypoidal adenocarcinomas like the one marked **A** classically present with occult bleeding and iron-deficiency anemia rather than acute obstruction?
A. Right-sided adenocarcinomas have inherently lower rates of lymphovascular invasion, limiting their ability to cause acute bleeding
B. The polypoidal morphology of right-sided tumors preferentially invades the submucosa, sparing the muscular wall and preventing stricture formation
C. The fungating surface of right-sided masses produces mucus that coats the tumor and prevents contact bleeding, leading only to slow chronic ooze
D. The right colon has a wider luminal diameter and more liquid fecal contents, allowing the mass to grow exophytically without causing mechanical obstruction until late stages
Explanation
Why option 1 is right
Right-sided colorectal cancers (cecum, ascending colon) present as polypoidal/exophytic fungating masses because the right colon has a wider luminal diameter and more liquid fecal contents. This anatomical difference allows the tumor to grow outward into the lumen without causing mechanical obstruction—obstruction occurs only late in the disease course. The friable, ulcerated surface of the fungating mass (as shown in structure A) bleeds chronically into the liquid stool, causing occult bleeding that manifests as iron-deficiency anemia with fatigue, dyspnea, and pallor. This is the classic presentation of right-sided polypoidal adenocarcinoma. (NCCN Colon Cancer Guidelines 2024; IDEA Trial NEJM 2018)
Why each distractor is wrong
Option 2: While submucosa invasion does occur, it is not the reason for the exophytic growth pattern or the classic presentation of occult bleeding. The luminal anatomy (width and stool consistency) is the primary driver of morphology and presentation, not invasion depth alone.
Option 3: Lymphovascular invasion rates do not explain why right-sided tumors present with chronic occult bleeding rather than acute obstruction. The presentation is determined by luminal anatomy, not by invasion patterns.
Option 4: Fungating masses do NOT produce a protective mucus coat that prevents bleeding. In fact, the friable, ulcerated surface of the fungating mass is inherently prone to contact bleeding, which is why occult bleeding is the hallmark presentation.
