A usually large cell non-Hodgkin lymphoma of B-cell phenotype, arising from the anus. Lymphomas originating from the anal region are rare in the general population, but they are seen with a higher frequency in HIV-positive patients, particularly homosexual men. The disease is anus lymphoma (Monarch Disease Ontology term MONDO_0001888). Also known as: anal lymphoma, lymphoma of anus, lymphoma of the anus, primary anal lymphoma.