Gastric Polyps

Description

• Mostly benign with minimal malignant potential
• Most commonly discovered as asymptomatic incidental findings on upper endoscopy (esophagogastroduodenoscopy [EGD])
• Different types based on origin:
  • Epithelial (most common): fundic gland, hyperplastic, adenomas
  • Endocrine: carcinoid tumors
  • Infiltrative: xanthomas and lymphoid proliferations
  • Mesenchymal: gastrointestinal stromal tumor (GIST), leiomyoma, fibroma, lipoma
  • Inflammatory fibroid polyp

Epidemiology

Incidence

• Incidence ~6% in the United States (1)
• Male = female (1:1)
• Frequency of polyp types:
  • Fundic gland: 13–77%
  • Hyperplastic: 18–70%
  • Adenoma: 0.5–3.75%
  • Carcinoid: <2%
  • Xanthoma: 0.3–3.9%
  • GIST: 1–3%
  • Inflammatory fibroid: 0.1–3%
  • Hamartomas: <1%
  • Others: <1%

Prevalence
Prevalence varies worldwide, estimated to be ~4% in United States. Fundic gland polyps (often arising in the setting of long-term proton pump inhibitor [PPI] use) are the dominant type. Polyps associated with Helicobacter pylori gastritis (hyperplastic and adenomatous) have become less common. Fundic gland polyps represent ~80% of polyps.

Geriatric Considerations
2/3 of gastric polyps are in patients >60 years old.

Pediatric Considerations
Gastric polyps are common in both children and adults with familial adenomatous polyposis (FAP) syndrome. Most often, these are fundic gland polyps.

Etiology and Pathophysiology

• Fundic gland polyp
  • Sessile lesion usually <0.5 cm; found throughout the stomach
  • Most occur sporadically.
  • Associated with polyposis syndromes (FAP, MUTYH-associated polyposis [MAP], and gastric adenocarcinoma and proximal polyposis of the stomach [GAPPS])
  • Very low risk for malignancy (except in FAP syndrome)
  • Associated with long-term PPI use
  • Histology shows dilated oxyntic glands, lined by flattened parietal and mucous cells.
• Hyperplastic polyp
  • Smooth, rounded (typically multiple) lesions, usually in the antrum
  • 0.5 to 1.5 cm—can be much larger
  • Hyperregenerative response of epithelium due to chronic inflammation (most commonly H. pylori)
  • Low risk for malignancy
    • Risk of malignancy in hyperplastic polyps increases with size (>1 cm) and pedunculation.
    • Loss of p16 and increased Ki-67 expression may indicate dysplasia in hyperplastic polyps.
• Adenomatous polyp (raised intraepithelial neoplasia)
  • Typically associated with chronic atrophic gastritis
  • Velvety, lobulated, usually solitary lesion; most often found in the antrum; <2 cm
  • Considered to be premalignant
    • Malignant potential depends on size (>2 cm with 40–50% risk of malignant transformation) and degree of dysplasia and villous component.
• Carcinoid polyp
  • Clusters of mucosal enterochromaffin cells; most often in the corpus or fundus
  • Derived from enterochromaffin-like (ECL) cells
  • Risk for metastasis depends on size.
  • Four distinct subtypes (type 1 most common)
• Xanthoma
  • Small, yellow nodules or plaques that protrude from the surrounding pink gastric mucosa
  • Lipid-laden macrophages containing cholesterol and neutral fat embedded in the lamina propria
  • No malignant potential
• GISTs
  • Neoplastic proliferations of interstitial cells of Cajal (or their precursors)
  • Well-circumscribed, submucosal lesions; most often in the fundus; median size 6 cm
  • Varying malignant potential based on size and mitotic activity
  • 50% of patients with GISTs >2 cm have metastatic disease at the time of presentation (usually liver).
• Inflammatory fibroid polyp
  • Originates from submucosa; frequently with central depression or ulceration; 1 to 5 cm
  • No malignant potential
• Hyperplastic and adenomatous polyps are associated with any inflammatory process causing chronic cell turnover.
• Hamartomas
  • Abnormal growth of otherwise normal tissue
  • Benign; rarely invade or compress surrounding structures
• All others: no known causes

Genetics

• Most polyps have no known hereditary component.
• Fundic gland polyps are associated with FAP arising from APC gene mutation.

Risk Factors

• Increased incidence with age
• Chronic gastritis: hyperplastic polyps
  • Chronic NSAID use, increased gastric secretions, erosions, or ulcers
• Hypergastrinemia (gastrinoma, Zollinger-Ellison syndrome, long-term PPI use): fundic gland polyps
• H. pylori: hyperplastic and adenomatous polyps
• BRAF inhibitors used to treat melanoma may increase the risk for hypertrophic gastric polyps.

Commonly Associated Conditions

• Associated with certain familial syndrome (1)[C]
  • Fundic gastric polyps: FAP
  • Hamartomas: Peutz-Jeghers syndrome, juvenile polyposis, Cronkhite-Canada syndrome, Cowden disease
• Carcinoid polyps:
  • Type 1: achlorhydria, hypergastrinemia, and pernicious anemia
  • Type 2: Zollinger-Ellison syndrome, MEN1 syndrome