Colorectal polyps

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Colorectal polyps



Colorectal polyps


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USMLE® Step 1 questions

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Colorectal polyps

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USMLE® Step 1 style questions USMLE

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A 5-year-old boy is brought to the physician by his mother due to excessive fatigue over the past 2 months. The mother has occasionally noticed blood in the toilet bowl after the patient defecates. There is no significant family history of cancers. The patient's temperature is 37.0°C (98.6°F), pulse is 96/min, and blood pressure is 110/70 mmHg. Physical examination shows conjunctival pallor. No abnormal skin pigmentation is noted. Laboratory results are as follows:

 Laboratory Value  Result 
 Hemoglobin  9.7 g/dL 
 Hematocrit  35% 
 Mean corpuscular volume (MCV)  74 μm3 
Colonoscopy is performed and reveals seven polyps throughout the gastrointestinal tract; subsequent biopsy reveals hamartomatous mucosal polyps. Genetic testing is performed and reveals a mutation in the BMPR1A gene. Which of the following is the most likely diagnosis in this patient? 

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Adenomatous colonic polyps p. 396

APC gene p. 222

adenomatous colonic polyps and p. 396

Colonic polyps p. 396

Hamartomatous colonic polyps p. 396

Hyperplastic polyps p. 396

KRAS gene p. 222

adenomatous colonic polyps and p. 396


A colorectal polyp is a small clump of epithelial cells that form a small bump or overgrowth of tissue along the lining of the colon or rectum.

The cells lining the colon and rectum are constantly dividing, and typically when there’s an overgrowth of tissue it’s benign, but some can become malignant, meaning that the dividing cells can start invading nearby tissues over time.

There are various types of colorectal polyps.

The most common ones are adenomatous polyps, also called colonic adenomas.

They form when there is a mutation in the adenomatous polyposis coli gene or APC gene, which is a tumor suppressor gene that regulates cell growth.

When the APC gene is mutated, the epithelial cells start to quickly divide forming polyps.

But even though they are dividing, these polyps only become malignant - meaning they only invade nearby tissues if there are additional mutations in other tumor suppressor genes like the p53 gene or in proto-oncogenes like K-Ras.

Some people with a genetic condition called familial adenomatous polyposis syndrome or FAP are born with a mutation in their APC gene, and they end up developing hundreds or even thousands of polyps in their colon.

These people often need to have their entire colon surgically removed because having so many polyps increases the chance that one cell among all of those polyps will develop another mutation and become malignant.

Adenomatous polyps can also be classified histologically based on their growth pattern as being tubular where the growth has little holes within it looking at a cross section of tissue or a tube if you imagine it in three dimensions or villous where the growth looks like a little tree with branches.


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  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Colon Polyps" JAMA (2008)
  6. "Colorectal Cancer: Epidemiology, Risk Factors, and Health Services" Clinics in Colon and Rectal Surgery (2005)
  7. "Serrated polyps of the large intestine: current understanding of diagnosis, pathogenesis, and clinical management" Journal of Gastroenterology (2012)

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