Primary splenic lymphoma: does it exist?

The number of primary splenic lymphomas being reported is increasing despite the rarity of this malignancy, but what really constitutes a lymphoma arising primarily in the spleen is still a matter of discussion. The authors choose the "restrictive" definition of a lymphoma involving the spleen and the splenic hilar lymph nodes only. In this way, the risk of epidemiologic or clinical overestimation is avoided. The clinical features of this condition are characterized by non specific symptoms and signs, while the prevailing histology is that of a low-grade or intermediate-type lymphoma. Disease spreading outside of the spleen and its hilar lymph nodes is the single most important factor associated with an unfavorable prognosis. From this usual clinical picture, two distinct nosologic entities can be outlined on the basis of histologic and immunologic peculiarities: splenic lymphoma with circulating villous lymphocytes and marginal-zone splenic lymphoma. The former arises from follicular center cells and is characterized by hypersplenism, variable percentages of circulating villous lymphocytes and, frequently, a monoclonal gammopathy. The latter originates from a peculiar splenic B-cell structure separated by the mantle zone. The proliferating cells are medium-sized KiB3-positive lymphocytes with round or cleaved nuclei and pale cytoplasm, which surround follicular centers and infiltrate the mantle zone. It is interesting that marginal-zone lymphoma cells share some of the characteristics of the lymphocytes involved in both lymphomas of mucosa-associated lymphoid tissue and the B-monocytoid lymphomas. Splenectomy is still the most effective therapy for all primary splenic lymphomas.