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The inflammatory spectrum of gastric diseases includes different clinico-pathological entities, the etiology of which was recently established in the international Kyoto classification. A diagnosis of gastritis combines the information resulting form the gross examination (endoscopy) and histology (microscopy). It is important to consider the anatomical/functional heterogeneity of the gastric mucosa when obtaining representative mucosal biopsy samples. Gastritis includes self-limiting and non-self-limiting (long-standing) inflammatory diseases, and the latter are epidemiologically, biologically and clinically linked to the onset of gastric cancer (i.e. "inflammation-associated cancer"). Different biological models of inflammation-associated gastric oncogenesis have been proposed. Helicobacter pylori (H. pylori) gastritis is the most prevalent worldwide, and H. pylori is classified as a first-class carcinogen. On these bases, eradicating H. pylori is mandatory for the primary prevention of gastric cancer. Non-self-limiting gastritis may also be triggered by the immune-mediated destruction of gastric parietal cells, resulting in autoimmune gastritis. In both H. pylori-related and autoimmune gastritis, the non-self-limiting inflammation results in atrophy of the gastric mucosa, which is the main factor promoting gastric cancer. Long-term follow-up studies consistently demonstrate the prognostic impact of the histological staging of gastritis in gastric cancer secondary prevention strategies.

Gastric intraepithelial neoplasia (IEN; formerly dysplasia) is an advanced precancerous lesion. Lesions indefinite for IEN mimic the IEN phenotype but lack some morphologic attributes of IEN. Indefinite for IEN lesions may arise in native foveolae (atypical foveolar hyperproliferation [aFH]) or intestinalized glands (hyperproliferative intestinal metaplasia [HIM]). The clinicopathologic outcome of such lesions is debated. We retrospectively studied the clinicopathologic behavior of 129 consecutive indefinite for IEN lesions (HIM, 98; aFH, 31; median follow-up, 31 months) and correlated outcome with the extent and topography of mucosal atrophy (assessed by OLGA staging) at the initial endoscopy/biopsy. At enrollment, aFH never coexisted with severe/extensive atrophy (all cases were in low-risk OLGA stages [0-II]), whereas HIM was associated with low- and high-risk OLGA stages (0-II, 73; III-IV, 25). At follow-up, IEN was never documented among cases enrolled as aFH, while follow-up endoscopy/biopsy documented 6 neoplastic intraepithelial lesions among 98 cases of HIM (6%, all had high-risk OLGA stages at initial biopsy). OLGA staging can stratify indefinite for IEN lesions into different risk classes, potentially contributing to decisions for a patient-specific follow-up strategy.

Gastritis is defined as inflammation of the gastric mucosa. In histological terms, it is distinguishable into two main categories, i.e. non-atrophic and atrophic. In the gastric mucosa, atrophy is defined as the loss of appropriate glands. There are several etiological types of gastritis, their different etiology being related to different clinical manifestations and pathological features. Atrophic gastritis (resulting mainly from long-standing Helicobacter pylori infection) is a major risk factor for the onset of (intestinal type) gastric cancer. The extent and site of the atrophic changes correlate significantly with the cancer risk. The current format for histology reporting in cases of gastritis fails to establish an immediate link between gastritis phenotype and risk of malignancy. Building on current knowledge of the biology of gastritis, an international group of pathologists [Operative Link for Gastritis Assessment (OLGA)] has proposed a system for reporting gastritis in terms of its stage (the OLGA Staging System): this system places the histological phenotypes of gastritis on a scale of progressively increasing gastric cancer risk, from the lowest (Stage 0) to the highest (Stage IV). The aim of this tutorial is to provide unequivocal information on how to standardize histology reports on gastritis in diagnostic practice.