IMMUNOHISTOCHEMICAL CHARACTERIZATION OF MAST-CELL DISEASE IN PARAFFINSECTIONS USING TRYPTASE, CD68, MYELOPEROXIDASE, LYSOZYME, AND CD20 ANTIBODIES

To date, the diagnosis of mast cell disease (MCD) relied on routine pl us histochemical stains. Its differential diagnosis, however, includes a variety of other hematopoietic and particularly B-cell lymphoid neo plasms that are best identified in paraffin sections using immunostain s. To determine the paraffin-section immunoreactivity of MCD, 20 speci mens from 14 patients with MCD and 1 bone marrow sample (from a patien t with probable MCD) that showed equivocal metachromasia, were stained with antitryptase, CD68 (KP-1), CD20 (L26), antilysozyme, and antimye loperoxidase antibodies. Ten hairy cell leukemias (HCLs), six lymphoma s of parafollicular and/or monocytoid B-cell (MBCLs) and low-grade muc osa-associated lymphoid tissue (MALT) types, six granulocytic sarcomas , and five acute myeloid leukemias with monocytic differentiation (M4 and M5 types) were also stained. Tryptase positivity was identified in all of the MCD cases. The staining was moderate to strong in 20 of th e 21 specimens, including the probable MCD case. No other neoplasms te sted were tryptase positive. CD68 showed similar to even stronger stai ning in all of the specimens of MCD, HCL, granulocytic sarcoma, and ac ute myeloid leukemia (M4 and M5 types) tested and in five of the six M BCL and/or MALT-type lymphomas, Weak-to-moderate lysozyme staining see med to be present in at least 7 of the MCD specimens, whereas there wa s a lack of staining for myeloperoxidase in 12 specimens, and 7 specim ens were nonevaluable (1 case was not tested). Myeloperoxidase was ide ntified in all of the granulocytic sarcomas and acute myeloid leukemia s (M4 and M5 types) but not in any HCLs, MBCLs, or low-grade lymphomas of MALT type. CD20 was negative in all of the MCD and myelomonocytic neoplasms but positive in all of the HCLs, MBCLs, and low-grade B-cell lymphomas of MALT type. IMCD, therefore, has a characteristic tryptas e-positive, CD68-positive, and CD20-negative phenotype in paraffin sec tions. This distinguishes MCD from the hematopoietic and/or lymphoid d isorders that it most closely resembles.