THE VALUE OF IMMUNOHISTOCHEMISTRY
IN THE ASSESSMENT OF BONE MARROW DISORDERS
Attilio Orazi, M.D., FRCPath. and Dennis P. O'Malley, M.D.
Systemic mastocytosis is a rare disease characterized by a generalized infiltration of mast cells involving
many organs, most notably the bone marrow, spleen, liver and lymph nodes; cutaneous involvement may or may
not be present. An association with malignant hematopoietic disorders has been recognized. In the bone
marrow, characteristic findings include the presence of clusters of pale cells with oval or reniform nuclei,
eosinophilia, and the presence of fibrosis. Although the diagnosis is usually established after special
stains with Giemsa or toluidin blue, the mast cells can also be immunostained with c-KIT and CD68/KP-1
monoclonal antibodies. Special stain for CAE, which is frequently used to identify mast cells in
extramedullary sites (e.g. skin), is inhibited by nitric acid decalcification and is therefore not used to
stain marrow biopsies that are so processed . Mast cells are also positive, in most cases, with an antibody
to tartrate resistant acid phosphate (TRAP). Anti-tryptase, a recently available antibody, has also been
shown to be of value in the diagnosis of mast cell disorders (Horny et al, 1998). In cases of malignant
mast cell disease, the anti-tryptase antibody can correctly identify as mast cells a higher proportion of
the malignant cells than CAE or Giemsa. Chymase is another recently proposed marker for mast cells. We
have had yet no direct experience with these reagents.
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disease in paraffin sections using tryptase, CD68, myeloperoxidase, lysozyme, and CD20 antibodies. Mod