Gastrointestinal lymphomas: entities and mimics.

The gastrointestinal tract is the most common extranodal site of lymphoma involvement. Although B-cell lymphomas are by far the most frequent type found in this location, gastrointestinal lymphomas are a diverse group of neoplasms, many of which are characterized by distinctive clinicopathologic settings. Diffuse large B-cell lymphoma and marginal-zone lymphoma of mucosa-associated lymphoid tissue are commonly encountered, but other less-common entities can pose diagnostic challenges, mimicking both benign, reactive conditions and each other. We describe several different lymphoma subtypes, with a focus on frequently encountered challenges in differential diagnosis.