B

m tTt

Fig. 3.23 A, B Examples of low-grade intraepithelial neoplasia of flat gastric mucosa. The atypia extends to the surface.

ing; there is no stromal invasion. Mucin secretion is absent or minimal. The pleo-morphic, hyperchromatic, usually pseu-dostratified nuclei often are cigar-shaped. Prominent amphophilic nucleoli are common. Increased proliferative activity is present throughout the epithelium.

Progression of intraepithelial neoplasia to carcinoma

Carcinoma i s diagnosed when the tumour invades into the lamina propria (intramu-cosal carcinoma) or through the muscu-laris mucosae. Some gastric biopsies contain areas suggestive of true invasion (such as isolated cells, gland-like structures, or papillary projections). The term 'suspicious for invasion' is appropriate when the histological criteria for an invasive malignancy are equivocal. Up to 80% of intraepithelial neoplasias may progress to invasion. Indeed, inva sive cancer already may be present in patients found to have high-grade intra-epithelial neoplasia with no obvious tumour mass. The extent of intestinal metaplasia associated with intraepithelial neoplasia, together with a sulphomucin-secreting phenotype of the intestinalized mucosa (type III intestinal metaplasia), correlate with an increased risk of carcinoma development.

Adenomas

Adenomas are circumscribed, benign lesions, composed of tubular and/or vil-lous structures showing intraepithelial neoplasia. The frequency of malignant transformation depends on size and his-tological grade. It occurs in approximately 2% of lesions measuring < 2 cm and in 40-50% of lesions > 2 cm. Flat adenomas may have a greater tendency to progress to carcinoma.

Polyps

Hyperplastic polyps

Hyperplastic polyps are one of the commonest gastric polyps. They are sessile or pedunculated lesions, usually < 2.0 cm in diameter, typically arising in the antrum on a background of H. pylorigas-tritis. They contain a proliferation of surface foveolar cells lining elongated, distorted pits extending deep into the stroma. They may contain pyloric glands, chief cells and parietal cells. The surface often erodes. In a minority of cases, carcinoma develops within the polyps in areas of intestinal metaplasia and dys-plasia.

Fundic gland polyps

Fundic gland polyps are the commonest gastric polyp seen in Western populations. They occur sporadically, without a relationship to H. pylori gastritis. They also affect patients on long-term proton pump inhibitors or patients with familial adenomatous polyposis (FAP), who may have hundreds of fundic gland polyps {2064, 2065}.

The lesions consist of a localized hyperplasia of the deep epithelial compartment of the oxyntic mucosa, particularly of mucous neck cells, with variable degrees of cystic dilatation. Sporadic fundic gland polyps have no malignant potential. Exceptionally, patients with attentuated FAP may develop dysplasia and carcinoma in their fundic gland polyps {2214, 1204}

Polyposis syndromes

Peutz-Jeghers polyps, juvenile polyps, and Cowden polyps generally do not occur spontaneously, but rather as part of hereditary polyposis syndromes. In the stomach, Peutz-Jeghers polyps are characterized histologically by branching bands of smooth muscle derived from

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