Advancing the Science in Gastric Pre-Neoplasia: Study Design Considerations.

Gastric cancer is the third leading cause of cancer-related mortality and the leading infection associated cancer worldwide. In the US, there are estimated 27,510 new cases and 11,140 gastric-cancer related deaths in 2019.1 Gastric adenocarcinoma (GA) is the most common form of gastric cancer. Histologically, by the Lauren classification, GA can be divided to two types: intestinal GA and diffuse GA.2 The Cancer Genome Atlas (TCGA) initiative has identified 4 molecular subtypes of gastric cancers: genomically stable (diffuse), chromosomally stable (intestinal), microsatellite instability, and Epstein-Barr virus subtypes.3 GA is also classified based on anatomic location into cardia (CGA) or non-cardia GA (NCGA). NCGA include those arising from the antrum, incisura, body, and/or fundus.4 Intestinal-type NCGA (hereafter simply referred to as “NCGA”) results from the complex interaction between genetic, environmental, and microbial determinants, which drive the stepwise progression through a series of discrete histopathologic stages, the “Correa cascade”, from non-atrophic gastritis to gastric preneoplasia (chronic atrophic gastritis (AG), gastric intestinal metaplasia (GIM)) and dysplasia, prior to malignant transformation to invasive adenocarcinoma in a minority of patients (1–3%). Helicobacter pylori (H. pylori) is the dominant factor in this cascade with an attributable risk of 75–88% but additional pathways are recognized.5, 6 Most factors which account for the prevalence of GIM and its progression to neoplasia lack definitive evidence. Despite the established association of GIM with increased risk of incident NCGA, currently it’s not possible to predict who will develop gastric neoplasia. Furthermore, whether the endoscopic surveillance of GIM to detect early NCGA compared to no surveillance may improve patient-related outcomes, has not been established, particularly in low incidence countries like the US. Whether selected surveillance of GIM for identifiable high-risk groups within, such as racial/ethnic minorities and immigrants, is similarly unclear. These critical knowledge gaps formed the rationale behind the American Gastroenterological Association’s (AGA) Clinical Practice Guideline Committee’s constructing evidence-based guidelines to inform the management of patients who are diagnosed with GIM based on gastric biopsies performed in routine clinical practice. The technical review team systematically summarized and synthesized the literature to inform pre-defined clinical questions proposed by the AGA guideline panel using standard systematic review methodology. With guidance from the guideline committee, we developed a comprehensive list of direct and indirect evidence needed to inform the guideline questions. The direct evidence included randomized and non-randomized comparative studies that assessed the benefits and/or harms of endoscopic surveillance in patients with GIM. The indirect evidence included the prevalence of GIM, the incidence of intestinal-type NCGA in individuals with GIM, and specified risk factors and biomarkers associated with the development of NCGA in patients with GIM: family history of gastric cancer, racial/ethnic background, immigration status, smoking history, pernicious anemia and/or autoimmune atrophic gastritis, GIM topographic extent, GIM histological subtype, and predictive biomarkers (e.g., H. pylori and its virulence factors (e.g. cagA and vacA), and the pepsinogens). Our systematic literature search did not identify studies that provide direct evidence to inform our clinical questions, although we were able to identify many studies that informed our questions indirectly. It was evident that there was inconsistent and incomplete methodology among the studies and many publications were missing essential demographic, clinical, endoscopic and/or pathology data. These data elements are necessary to allow a thorough assessment of the events reported and to determine the certainty of that evidence. The lack of direct evidence and the lack of certainty in the indirect evidence limited the guideline’s panel ability to make strong recommendations for a common clinical condition. To stimulate the field to improve clinical outcomes, best practices are intended to guide future research and overcome the limitations of the available evidence. The aim of this guidance document is to highlight the methodological limitations that the technical review and guideline team encountered in the literature review and provide guidance for future design of high quality studies on GIM as a premalignant finding that is associated with development of gastric cancer. We have provided a general checklist that will facilitate standardization of future studies to advance the science of GIM with rigorous evidence to inform clinical care. For completeness, we include measures that are important yet were outside the scope of the AGA GIM technical reviews and guidelines (e.g., endoscopy imaging).