MIC2 is characteristically expressed in lymphoblastic lesions and Ewing's/
primitive neuroectodermal tumor sarcomas. Although MIC2 has recently been reported in
chloroma and rare
terminal deoxynucleotidyl transferase-positive
acute myelogenous leukemia (AML), the incidence and the significance of MIC2 (CD99) immunoreactivity in myeloid lesions is not clear. In this study, we evaluated MIC2 positivity in a variety of myeloid diseases and normal marrow to determine its incidence and distribution in myeloid diseases; its correlation with flow cytometric and cytogenetic data in AML; and its association with leukemic transformation, relapse, and
chloroma formation.
Paraffin sections of 11
chloromas and 94 bone marrow core biopsies from 66 patients were stained with CD99
monoclonal antibody 12E7. Of 94 bone marrow core biopsies, there were 30 AML (fragment
antigen binding M0 to M6), 23 remissions, 5 relapses, 12
myeloproliferative disorders, 13
myelodysplastic syndromes, and 11 normal marrows from patients who did not have
leukemia. CD99 immunoreactivity was evaluated with light microscopy. MIC2 expression was seen in leukemic blasts in 6 of 11
chloromas (55%) and 13 of 30 AML (43%) but rarely in
myeloproliferative disorders,
myelodysplastic syndromes, remission, and normal marrow. CD99 tended to be positive in M1-, M3-, and
HLA-Dr-negative AML and negative in AML with relapse. MIC2 expression did not correlate with the karyotype independent of French-American-British Cooperative Group classification and the disease remission or occurrence of
chloroma in AML. We concluded that MIC2 is commonly expressed in leukemic blasts of AML and is not predictive of leukemic transformation from
myeloproliferative disorders and
myelodysplastic syndromes or
chloroma formation. Caution should be taken when using MIC2 as a marker for
Ewing's sarcoma/
primitive neuroectodermal tumor or
lymphoblastic lymphoma on
paraffin sections of either soft tissue or bone marrow specimens.