Nucleolated cells in extranodal marginal zone lymphoma: a case report and discussion of circulating lymphoma cells with prominent nucleoli.

Various types of lymphoma/leukemia can present with leukemic involvement by neoplastic cells with prominent nucleoli. Patients with chronic lymphocytic leukemia (CLL) most commonly can present in this fashion but other, less common types include mantle cell lymphoma, splenic marginal zone lymphoma, splenic diffuse red pulp small B-cell lymphoma, and splenic B-cell lymphoma/leukemia with prominent nucleoli (SBLPN). The latter is a newly proposed category in the fifth edition of the World Health Organization classification of hematolymphoid neoplasms. This category includes most cases that were previously designated hairy cell leukemia-variant and rare cases of CD5-negative B-prolymphocytic leukemia. A case of extranodal marginal zone lymphoma (EMZL) is reported to highlight the presence of nucleolated lymphocytes in the peripheral blood and bone marrow and their impact on the differential diagnosis, particularly with SBLPN. An 80-year-old woman with a reported history of "CLL", diagnosed and treated with clinical remission, developed gastric EMZL which relapsed twice after chemotherapy. At time of last relapse, a peripheral blood smear and bone marrow aspiration and biopsy specimens were evaluated to assess the presence and extent of blood and bone marrow involvement. The pathologic findings and differential diagnosis are discussed. A complete blood count showed a leukocyte count of 7.9 × 10/L and review of the peripheral blood smear showed 32% nucleolated lymphocytes (absolute lymphocyte count, 2.5 × 10/L). Bone marrow aspiration and biopsy showed a nodular, interstitial, and focal sinusoidal lymphoid infiltrate with a subset of lymphocytes displaying nucleoli. Flow cytometry immunophenotypic analysis of the bone marrow showed a CD5-negative, monotypic small B-cell population consistent with extranodal MZL. This case illustrates that nucleolated lymphocytes can be observed in the peripheral blood smear of patients with EMZL. These findings expand the differential diagnosis of circulating nucleolated lymphocytes in the blood.