In the World Health Organization classification, one major and four minor criteria are specified for the diagnosis of systemic mastocytosis. We report our experience using these criteria to diagnose systemic mastocytosis involving bone marrow. A total of 59 patients with clinically suspected systemic mastocytosis underwent comprehensive bone marrow examination, including immunophenotyping by immunohistochemistry and/or flow cytometry and molecular studies for KIT exon 17 mutations. Serum tryptase levels were also assessed. Of these 59, 53 (90%) patients met the diagnostic criteria for systemic mastocytosis. In these patients, multifocal dense infiltrates of mast cells, the major criterion, was observed in 36 (68%) patients. Atypical mast cell morphology was observed in 53 (100%), an aberrant immunophenotype was identified in 50 of 52 (96%), KIT mutation was present in 33 of 44 (75%), and an elevated serum tryptase (420 ng/ml) was detected in 44 of 52 (85%). In the six patients in which bone marrow examination could not confirm systemic mastocytosis, one had systemic mastocytosis involving spleen, one patient had chronic idiopathic myelofibrosis, and four had no specific diagnosis, but systemic mastocytosis was still considered most likely. Of these six patients, atypical mast cell morphology was identified in five, aberrant immunophenotype in five, KIT mutation in two, and elevated serum tryptase in two. None of these cases met the major criteria. We conclude that the World Health Organization criteria are useful for the diagnosis of systemic mastocytosis in bone marrow specimens. The results also show the relative values of traditional morphologic criteria (ie, major criterion) and the results of ancillary testing (ie, minor criteria). However, as illustrated by the case of splenic systemic mastocytosis as well as the patient with chronic idiopathic myelofibrosis, the current World Health Organization system is neither completely sensitive nor specific for systemic mastocytosis.

Serum thymidine kinase 1 (TK1) levels have been reported to have prognostic significance in patients with chronic lymphocytic leukemia (CLL). Until recently, serum TK1 levels were assessed using inconvenient radioenzyme assays. In this study, we used a novel chemiluminescence assay to assess serum TK1 levels in patients with CLL at the time of first examination. We show that high serum TK1 levels predict poorer overall survival and correlate with unmutated immunoglobulin variable region genes, CD38 and ZAP-70 expression, and subsequent risk of developing large B-cell lymphoma (Richter syndrome). Similar findings were observed in a subset of patients treated with current fludarabine-based chemotherapy regimens. We suggest that serum TK1 levels analyzed using this convenient chemiluminescence assay may be useful in the risk assessment of patients with CLL.

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Rosai-Dorfman disease is a rare histiocytic disorder shown to have gene mutations that activate the MAPK/ERK pathway in at least one-third of cases. Most patients with Rosai-Dorfman disease present with bulky lymphadenopathy or extranodal disease, but rarely Rosai-Dorfman disease is detected concomitantly with lymphoma in the same biopsy specimen. The underlying molecular mechanisms of focal Rosai-Dorfman disease occurring in the setting of lymphoma have not been investigated. We report 12 cases of Rosai-Dorfman disease and lymphoma involving the same anatomic site. There were five men and seven women (age, 23 to 77 years) who underwent lymph node (n = 11) or skin (n = 1) biopsy; the lymphomas included nodular lymphocyte predominant Hodgkin lymphoma (n = 6), classical Hodgkin lymphoma (n = 4), small lymphocytic lymphoma (n = 1) and extranodal marginal zone lymphoma (n = 1). The foci of Rosai-Dorfman disease in all cases had S100 protein-positive histiocytes undergoing emperipolesis. No patients had Rosai-Dorfman disease at other anatomic sites at initial diagnosis and at last follow-up (median, 40 months). We performed immunohistochemical analysis to assess activity of the MAPK/ERK pathway in the Rosai-Dorfman disease foci. We also micro-dissected disease foci and analyzed 146 genes using next-generation sequencing in four cases with adequate DNA; the panel included genes previously reported to be mutated in Rosai-Dorfman disease. All cases were negative for gene mutations. Nevertheless, all cases were positive for cyclin D1 and most cases showed pERK expression indicating that the MAPK/ERK pathway is active in the histiocytes of focal Rosai-Dorfman disease. We conclude that focal Rosai-Dorfman disease coexisting with lymphoma is a clinically benign and localized histiocytic proliferation. These data also indicate that the MAPK/ERK pathway is active in focal Rosai-Dorfman disease although we did not identify activating mutations. These findings suggest that the pathogenesis of focal Rosai-Dorfman disease is different from that of usual cases of Rosai-Dorfman disease.

Context.-Mast cells of systemic mastocytosis (SM) have aberrant immunophenotypes that are useful for their detection by flow cytometry immunophenotyping.Objectives.-To assess the usefulness of CD2, CD25, and other antigens for establishing the diagnosis of SM in bone marrow using flow cytometry immunophenotyping.Design.-We studied 50 bone marrow aspirates of patients with SM using flow cytometry immunophenotyping. The bone marrow aspirates were stained with antibodies specific for CD2, CD25, CD35, CD59, CD63, and CD69. For the detection of CD2 and CD25, antibodies conjugated with phycoerythrin (PE) or fluorescein isothiocyanate (FITC) were compared. CD45-PerCP and CD117-APC were used for gating. Data were acquired on FACS Calibur cytometers and analyzed using CellQuest software.Results. Conclusions.-Flow cytometry immunophenotyping is a rapid and sensitive technique for characterizing mast cells in bone marrow aspirate specimens. The use of PEconjugated antibodies for CD2 and CD25 improves the detection rate (CD2) or facilitates analysis (CD25); therefore, PE-conjugated antibodies are suggested. Antibodies reactive with CD35, CD59, CD63, and CD69 are also helpful in detecting SM in bone marrow.