Reliable and Cost‐Effective Paraffin Section Immunohistology of Lymphoproliferative Disorders

We studied 110 neoplastic and reactive lymphoid proliferations with three monoclonal antibodies–CD20 (L26), CD43 (Leu22), and CD45RO (UCHL1)–on B5-fixed, paraffin-embedded tissue to evaluate the utility of this panel as an immunotypic screen of such lesions. All cases were initially immunotyped by conventional methods. Genotyping by Southern blot hybridization was also done in 54 cases. Seventy-four of 79 malignant lymphomas and both of two hairy cell leukemias were of B-cell origin; and five lymphomas were defined as T-cell lineage. Lineage assignment was identical for paraffin section immunohistology and conventional immunotyping in 73 of 76 B cell and all of five T-cell tumors. CD20 was reactive with 73 of 76 B-cell tumors. CD43 was reactive with 12 of 74 B-cell lymphomas, and CD20/CD43 coexpression was seen in 11 of these cases. CD43 and CD45RO marked all of five and three of five T-cell lymphomas, respectively. Lineage assignment was identical for paraffin immunohistology and genotyping in 48 of 50 cases with identifiable gene rearrangements. Twenty-four nonneoplastic and five Hodgkin's disease cases that were studied also showed similar immunoreactivity patterns by both paraffin and conventional immunotypic methods. This panel of three monoclonal antibodies is an efficient, cost-effective approach for immunotyping most lymphoid proliferations in paraffin sections. Nevertheless, the pathologist should always try to obtain fresh or frozen tissue to aid in resolving occasional discrepant cases, to establish clonality in morphologically ambiguous ones, and to profile prognostically important phenotypic deletions.