Immunohistochemical detection of CD10 in paraffin sections of hematopoietic neoplasms - A comparison with flow cytometry detection in 56 cases

Paraffin-section immunohistochemistry with heat-induced epitope retrieval using a newly characterized monoclonal antibody (clone 56C6) against the CD10 antigen was performed on 56 hematopoietic tumors previously studied for CD10 expression by flow cytometry. The cases included 33 precursor B-lymphoblastic leukemias, 10 acute myeloid leukemias, five precursor T-lymphoblastic leukemias, five follicular lymphomas, and three Burkitt cell leukemias. Forty of the 56 cases were CD10 positive by flow cytometry studies, including all five follicular lymphomas (100%); 30 of 33 (91%) cases of precursor B-lymphoblastic leukemias, two of three (66%) cases of Burkitt cell leukemias, two of five (40%) cases of precursor T-lymphoblastic leukemias, and none of the 10 cases of acute myeloid leukemia. Thirty-nine of the 40 (97%) flow cytometric CD10-positive cases also expressed CD10 by immunohistochemistry in formalin- or B5-fixed, paraffin-embedded tissue, with only one case of precursor B-lymphoblastic leukemia being positive by flow cytometry and negative by immunohistochemistry. The 16 CD10-negative flow cytometry specimens were all also negative by immunohistochemistry. Thirty-seven CD10 immunohistochemistry positive cases showed a diffuse membranous staining pattern and two cases demonstrated a Golgi staining pattern. The fixation methods (10% neutral buffered formalin versus B5) and decalcification did not affect the CD10 immunostaining results. This study demonstrates that the new CD10 monoclonal antibody clone 56C6 is a reliable marker for detection of CD10 antigen expression in formalin- and B5-fixed paraffin-embedded tissue after heat-induced epitope retrieval when compared with flow cytometry detection of fresh tissue samples.