**3. Pre-cancerogenous epithelial lesions**

#### **3.1. Adenoma**

Gastric adenomas are polypoid and typically solitary lesions. They commonly arise in a background of chronic atrophic gastritis with accompanied intestinal metaplasia. By definition, the epithelia of adenomas are neoplastic (intraepithelial neoplasia/dysplasia). Most of them show an intestinal differentiation (including goblet cells, Paneth cells) and look like a colon adenoma. According to the classification of colon adenoma, they can be subdivided into tubular, villous or mixed adenomas and into low-grade or high-grade intraepithelial neoplasia. A minor group of gastric adenomas shows gastric gland differentiation like foveolar (so-called type II dysplasia) or pyloric gland differentiation, a mixture of foveolar/intestinal like differentiation or (very rare) a predominant Paneth-cell differentiation.

### **3.2. Pyloric gland-adenoma**

Pyloric gland-adenoma usually arises in women and has a background of atrophic autoimmunegastritis. This type of adenoma is polypoid and show closely packed pyloric gland-like tubuli. The epithelia are cuboidal with round nuclei and pale cytoplasm. Immunohistochemically pyloric gland-adenoma shows common gastric mucin (MUC 5A/C and MUC6).

### *3.2.1. Clinical significance*

Adenomas must be removed with clear margins. Large adenomas (more than 2 cm) show a higher risk of malignancy.
