Adenomatous polyps

High malignant potential
- Tubular adenoma: < 5%
- Tubulovillous adenoma: ∼ 20%
- Villous adenoma: ∼ 50%

Mnemonic

Villous adenomas are villains because they have the highest malignant potential.

Hyperplastic polyps

Most common type of nonneoplastic polyp among those with low malignant potential
Histology: hyperplasia of normal cellular components with a sawtooth/serrated pattern of crypt epithelium
- No dysplasia, see Cellular adaptations

Inheritance: autosomal dominant (one-third of cases are due to de novo mutations)
Intestinal manifestations
- Polyps develop in the second/third decade of life but patients are usually asymptomatic until symptoms of colon cancer develop.
- Lifetime colorectal cancer risk: 100% (onset typically occurs at 35–40 years of age)
Diagnostic findings
- Sigmoidoscopy/colonoscopy and histology
  - 100 adenomatous polyps throughout the colorectum
  - Desmoid tumors
- Genetic testing: mutations in the tumor-suppressing APC gene

Inheritance: autosomal dominant
Intestinal manifestations
- Large polyps can manifest with abdominal pain, GI bleeding, or intestinal obstruction.
- Lifetime colorectal cancer risk: ∼ 40% (onset typically occurs at ∼ 45 years of age) and increased risk of other GI malignancies (e.g., small bowel, pancreatic, stomach cancer)
Extraintestinal manifestations
- Mucocutaneous hyperpigmented macules (i.e., lentigines) on the lips, buccal mucosa, genitals, palms, soles (seen in 95% of patients)
  - Due to affecting melanocytes, leading to the overproduction of melanin and the development of hyperpigmented macules.
- Increased risk of non-GI tract cancers (e.g., breast cancer, ovarian cancer)
Endoscopy and histology: hamartomatous PJS polyps throughout the GI tract
- PJS polyps are hamartomatous, with mucin-filled cystic spaces and significant smooth muscle proliferation.