The path(ology) from reflux oesophagitis to Barrett oesophagus to oesophageal adenocarcinoma

This review seeks to summarise the steps in the path from reflux oesophagitis to Barrett oesophagus to oesophageal adenocarcinoma. The epidemiology, clinical presentation, definitions, pathological features, diagnostic pitfalls, and emerging concepts are reviewed for each entity. The histological features of reflux oesophagitis can be variable and are not specific. Cases of reflux oesophagitis with numerous eosinophils are difficult to distinguish from eosinophilic oesophagitis and other oesophagitides with eosinophils (Crohn's disease, medication effect, and connective tissue disorders). In reflux oesophagitis, the findings are often most pronounced in the distal oesophagus, the eosinophils are randomly distributed throughout the epithelium, and eosinophilic abscesses and degranulated eosinophils are rare. For reflux oesophagitis with prominent lymphocytes, clinical history and ancillary clinical studies are paramount to distinguish reflux oesophagitis from other causes of lymphocytic oesophagitis pattern. For Barrett oesophagus, the definition remains a hotly debated topic for which the requirement for intestinal metaplasia to make the diagnosis is not applied unanimously across the globe. Assessing for dysplasia is a challenging aspect of the histological interpretation that guides clinical management. We describe the histological features that we find useful in making this evaluation. Oesophageal adenocarcinoma has been steadily increasing in incidence and has a poor prognosis. The extent of invasion can be overdiagnosed due to a duplicated muscularis mucosae. We also describe the technical factors that can lead to challenges in distinguishing the mucosal and deep margins of endoscopic resections. Lastly, we give an overview of targeted therapies with emerging importance and the ancillary tests that can identify the cases best suited for each therapy.