Splenic B-Cell Lymphoma/Leukemia, Unclassifiable in Japan

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 invol