Immunophenotyping of hematopoietic malignancies in paraffin sections.

Immunophenotyping of hematopoietic malignancies is usually accomplished in frozen sections or cell suspensions. To determine whether this procedure was also feasible in paraffin sections, we performed a double-blind immunoperoxidase study of 65 hematopoietic tumors whose phenotypes had been determined previously in fresh tissue. A selected antibody panel was used, including anti-LN2, UCHL-1, anti-cathepsin B, anti-Leu M1, anti-MB2, and anti-MT1. A correct phenotype was obtained on paraffin sections in 95% of cases. All 31 B-cell malignancies were properly classified, showing reactivity for LN2 and MB2. In 14 of 15 T-cell hematopoietic malignancies, all cells reacted with anti-MT1 and/or UCHL-1; the 1 case negative for these antigens was misdiagnosed as a B-cell tumor because of misinterpreted LN2 reactivity in benign histiocytes. Four of 5 true histiocytic neoplasms were positive for cathepsin B and LN2 but lacked other antigens; the fifth case was wrongly considered a B-cell proliferation because only bland histiocytes displayed cathepsin B. Only 1 of 7 Hodgkin's lymphomas was misdiagnosed (as a T-cell tumor); in the other 6 cases, Reed-Sternberg cells were reactive for LN2 and LEU M1. Five of 6 extramedullary myeloid leukemias also stained for LN2, MT1, and LEU M1. One showed LN2, MB2, and MT1; this case was classified as a B-cell neoplasm and indeed represented a pre-B-cell transformation of chronic myelogenous leukemia. These results show that the specified panel of antibodies may be useful for immunophenotyping of hematopoietic neoplasms when only paraffin sections are available for analysis. However, it cannot supplant traditional cell-marker studies of hematopoietic tumors because of its lesser accuracy.