Pathomorphological Diagnosis of Splenic Diffuse Red Pulp Small B-Cell Lymphoma

Abstract

Background. Unclassifiable splenic B-cell lymphoma/leukemia is a rare and poorly studied disorder introduced in the WHO classification of hematopoietic and lymphoid tissue malignancies for the first time in 2008. This type of lymphoma requires differential diagnosing between hairy cell leukemia-variant (HCL-V) and splenic diffuse red pulp small B-cell lymphoma (SDRPL). Aim. To develop criteria for diagnosis of SDRPL by comparison of bone marrow biopsies (BMB) and surgical specimens of the spleen. Methods. In the Department of Morbid Anatomy of the Hematology Research Center, preoperative BMBs and surgical specimens of the spleen (2013-2015) were compared in 71 patients (men/women ratio 1:2.6, age range 44-81, median age 58 years) using morphological and extended immunohistochemical studies. Sanger sequencing and PCR assay were carried out to analyze the mutational status of IgHV and to identify mutations in MAP2K1, NOTCH, BRAF. Results. SDRPL was diagnosed in 5 (7 %) of 71 patients. In 2 groups of patients (with normal and high WBC count), the morphological features of spleen tissue were similar to those of a neoplastic substrate of HCL-V. The immunohistochemical assay demonstrates monomorphic expression of CD20 and DBA.44 and heterogeneous expression of CD11c, TRAP, CD103, CD123 in all cases. In none of the 5 cases, expression of CD25, CD27, Cyclin D1, Annexin-1 was found. In bone marrow (unlike HCL and HCL-V), predominantly interstitial and intravascular scant CD20+ lymphoid infiltration (4 of 5 cases) was found without detectable nucleoli in nuclei of small lymphoid cells. In 1 case, there was a combined lymphoid infiltration: CD20+ microfocalinterstitial infiltration with an intravascular component. No persistent molecular mutations in the spleen tissue specimens were found. Conclusion. SDRPL is diagnosed in 7 % of splenic B-cell lymphomas. It is a rare disorder, whose verification requires an integrated approach taking into account clini cal and laboratory data, results of flow cytometry, cytological, morphological, extended IHC and molecular biological studies.