Paraffin section immunophenotype of cutaneous and extracutaneous mast celldisease - Comparison to other hematopoietic neoplasms

Mast cell disease (MCD) is a rare proliferation that may be easily confused with other hematopoietic tumors. Several paraffin section antibodies immun oreact with mast cells but most are not specific. Tryptase, a specific mark er of mast cells, may not be cost-effective to maintain in a laboratory bec ause of the rarity of these lesions. This study was undertaken to assess th e immunoreactivity of MCD and attempt to select a limited antibody panel fo r diagnosing MCD among hematopoietic tumors that morphologically mimic MCD. Immunophenotyping of cutaneous (10 cases) and extracutaneous (18 cases) MC D, as well as 94 other hematopoietic neoplasms, was performed on paraffin s ections. All cases of MCD showed strong and diffuse positivity for CD68 and tryptase. In the vast majority of the cases, the mast cells were also posi tive for CD117 (27 of 28) and CD43 (25 of 27). Four cases (40%) of cutaneou s MCD demonstrated a subpopulation of mast cells expressing myeloperoxidase (MPX), whereas all extracutaneous MCD were negative for MPX. Two (40%) ext ramedullary myeloid tumors (EMT) expressed CD43, CD68, CD117, and MPX, but none expressed tryptase. CD43, CD68, CD117, and tryptase were expressed by 25%, 1%, 15%, and 1%, respectively, of all B-cell lymphoid neoplasms, and n one expressed more than one of these four antigens. We conclude that (1) cu taneous MCDs may demonstrate a subpopulation of MPX antigen expressing tumo r cells and may be confused with cutaneous involvement by myeloid leukemia if other antibodies are not used; (2) tryptase is the most specific mast ce ll marker among the antibodies studied; and, (3) the detection of tryptase, together with CD68, CD117, and usually CD43, is unique to MCD among hemato poietic tumors.