Approximately 20 million gastrointestinal tract biopsies are performed each year in the United States. While many of these are straightforward, some are histologically subtle or involve a complex differential diagnosis. This concise visual guide to the full range of neoplastic gastrointestinal specimens provides the practicing pathologist or trainee with a clear analysis and diagnosis of both common and potentially misleading variants of disease. The authors cover the full tubular GI tract with over 600 high-quality images and a concise description of the key features of each entity: definitions and terminology, gross and morphologic features, differential diagnoses, useful ancillary tests, staging and grading parameters, and special clinical considerations. Images depict differential diagnosis features, frequently seen variants that can potentially lead to misclassification or misdiagnosis, and correlated molecular and immunologic techniques.