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5202 We here report the observation of the development of a splenic marginal zone lymphoma (SMZL) after years of active chronic visceral Leishmania (VL) infection, implying a possible pathogenic link between these two conditions, where the neoplastic process is preceded by a prolonged period of chronic antigen stimulation. In 2004, a 60-year old male developed attack-like episodes of septic fever with chills, rigor and subsequent profound fatigue. He had a 4 years previous medical history of severe asthma-like symptoms and hypereosinophilia. A bone marrow (BM) and liver biopsy were inconclusive. A whole-body computed tomography showed a moderately enlarged spleen. No evidence of bacterial, fungal or viral infection was found; the symptoms persisted, although mitigated, with occasional exacerbations over the following 3 years. By 2007 the patient was admitted again and a new BM biopsy was taken, still showing reactive changes. Due to increased splenomegaly, a diagnostic splenectomy was performed. Examination of the spleen revealed a primary splenic marginal zone lymphoma (SMZL). In 2010 the patient was admitted with septicaemia and constitutional symptoms. A BM biopsy showed the presence of numerous Leishmania amastigotes and a retrospective review of all previous biopsies (since 2004) identified Leishmania amastigotes in all of them. In fact, a thorough travel history covering the previous two decades revealed several visits, often twice a year, to the Mediterranean basin, e.g. Greece and Malta, areas endemic for Leishmania infantum (L. infantum). Visceral Leishmaniasis is a frequent opportunistic infection in HIV-infected immunodeficient individuals but uncommon in cancer patients, and only a few cases of VL in patients with already well-established malignant lymphoma have been reported. Chronic antigenic stimulation by microbial pathogens has been proposed as a pathogenetic factor in a variety of marginal zone lymphomas. Tissue specific immune responses toward Leishmania parasites have been shown in rodents, and the spleen is a ‘safe harbor’ for the long-term persistence of visceralizing Leishmania. Sustained antigenic stimulation with upregulation of critical signaling pathways may result in prolonged polyclonal B-cell proliferation, and a subsequent increased risk of malignant transformation. This case is the first to provide evidence for a possible link between chronic antigen stimulation by long-lasting L. infantum infection and the development of a SMZL. Disclosures: No relevant conflicts of interest to declare.