Splenic B-Cell Lymphoma/Leukemia, Unclassifiable in Japan
Authors: Suzuki Takaharu , Miyoshi Hiroaki , Kawamoto Keisuke , Shimono Joji , Takizawa Jun , Seto Masao , Ohshima Koichi 
Published: October 2019

Abstract
Introduction
Splenic B-cell lymphoma/leukemia, unclassifiable is defined as being unable to be classified as any other B-cell neoplasm infiltrating the spleen (World Health Organization Classification of Tumors of Haematopoietic and Lymphoid Tissue 2017). In splenic B-cell lymphoma/leukemia, unclassifiable, splenic diffuse red pulp small cell lymphoma (SDRPL) and hairy cell leukemia variant (HCL-v) are provisionally defined. The incidence of these diseases is rare. It has been reported that they account for 9% of splenic B-cell lymphomas (Haematologica 2010;95:1122-1129). There are no reports of histopathological examinations or BRAF mutations (V600E) in Japan. It has been shown that BRAF mutations (V600E) are found in all patients with Hairy cell leukemia-classical (HCL-c) (N Engl J Med. 2011 364: 2305-2315). This study aimed to clarify the pathological features of splenic B-cell lymphoma/leukemia, unclassifiable.
Methods
We analyzed 5 cases of suspected splenic B-cell lymphoma/leukemia, unclassifiable in terms of splenectomy. Five cases include 0 cases of SDRPL, 2 cases of HCL-v, and 3 cases of splenic B-cell lymphoma/leukemia, unclassifiable not applicable to either case. We analyzed patients undergoing splenectomy who were pathologically diagnosed at the Kurume University Pathology Course between July 2012 and May 2017. Splenic B-cell lymphoma/leukemia, unclassifiable was suspected in 5 cases. From the findings of peripheral blood, bone marrow, and BRAF mutation (V600E) analyses, 2 patients were diagnosed with HCL-v. The other 3 patients were diagnosed with splenic B-cell lymphoma/leukemia, unclassifiable. Pathological examinations were performed in these cases.
Marker expression analysis of the B-cell line was performed using immunohistochemical (IHC) staining and flow cytometry (FCM). IHC staining was performed on formalin-fixed paraffin-embedded samples. For FCM analysis, we confirmed the clonality of B cells and analyzed their expression. A positive judgment was made at 30% or greater. For BRAF mutation (V600E) analysis, deoxyribonucleic acid was extracted from formalin-fixed paraffin-embedded samples and performed using the Sanger sequencing method.
Results
The results of the analysis are shown in Table 1. HCL-v cases included 1 man and 1 woman, and the age was 62-71 years old. Splenic B-cell lymphoma/leukemia, unclassifiable cases included 2 men and 1 woman, and the age was 56-66 years. Splenic B-cell lymphoma/leukemia, unclassifiable cases involved bone marrow infiltration of B-cell lymphoma in 2 cases. In 3 cases of splenic B-cell lymphoma/leukemia, unclassifiable, there were no cases in which hairy cells were recognized in the peripheral blood. In all cases of splenic B-cell lymphoma/leukemia, unclassifiable, BRAF mutations (V600E) were not observed.
All cases of splenic B-cell lymphoma/leukemia, unclassifiable and HCL-v tested positive for cluster of differentiation (CD)20, CD19, and B-cell lymphoma (Bcl-2) and tested negative for CD103 and CD10. All HCL-v cases and 2 of 3 cases of splenic B-cell lymphoma/leukemia, unclassifiable tested positive for cyclin D3. One case of splenic B-cell lymphoma/leukemia, unclassifiable tested positive for CD5, but negative for lymphoid enhancer-binding factor 1 (LEF1), cyclin D1, and Sox11. All other cases tested negative for CD5, LEF1, cyclin D1, and Sox11. One of two cases of HCL-v and 2 of 3 cases of splenic B-cell lymphoma/leukemia, unclassifiable tested positive for CD11c. All HCL-v cases tested negative and 1 of 3 cases of splenic B-cell lymphoma/leukemia, unclassifiable tested positive for Bcl-6. IHC staining was performed because FCM was not performed in 1 case of HCL-v. There was no obvious bias in κ and λ. One patient with HCL-v who underwent FCM was κ-positive. Splenic B-cell lymphoma/leukemia, unclassifiable was κ-positive in all cases.
Conclusions
In this analysis, splenic B-cell lymphoma/leukemia, unclassifiable did not involve BRAF mutations (V600E) in all cases. It has been reported that cyclin D3 is highly expressed in SDRPL. Splenic B-cell lymphoma/leukemia, unclassifiable and HCL-v confirmed the same tendency (Blood. 2017; 129:1042-1045). Further molecular biological analysis for splenic B-cell lymphoma/leukemia, unclassifiable is desired.

Disclosures
No relevant conflicts of interest to declare.