Immunohistochemical evaluation of myeloid leukemia infiltrates (granulocytic sarcomas) in formaldehyde-fixed, paraffin-embedded tissue.

Paraffin sections of granulocytic sarcomas (GS) (n = 30) were immunohistochemically evaluated for CD3, CD15 (LeuM1), CD20 (L26), CD31, CD34, CD43, CD45, CD68 (KP1), lysozyme, myeloperoxidase (BM1), CD45RO (UCHL1), and LN5 with an avidin-biotin amplification system and a peroxidase-based color development system with DAB as a chromogen. CD45 positivity was present in all lymphomas and 24 of 25 granulocytic sarcomas. Lysozyme and CD43 labeled 26 of 29 granulocytic sarcomas, showing intense cytoplasmic staining. LN5 (membrane-staining) and CD68 (subtle cytoplasmic caplike staining) were found in 20 of 30 cases, often only focally. BM1 and CD15 mainly labeled maturing granulocytes and mostly were negative in primitive myeloid cells. Myeloid progenitor cell antigens CD31 and CD34 were seen in 7 and 12 of 30 cases, respectively. They seemed to recognize different subsets of myeloid leukemia infiltrates (16 cases positive for at least one); the use of CD31 and CD34 for defining these subsets should be evaluated further. Features suggesting a dual phenotype--T-cell and myeloid (positive for CD3, CD68, and lysozyme)--were documented in two cases. In contrast, lymphoblastic lymphomas (n = 4) were positive for CD3 and CD43 but negative for CD68, lysozyme, CD31, CD34, LN5, and myeloperoxidase. Lymphocytic lymphomas (n = 10) were positive for CD20 and CD43 but negative for all other markers. Small, round-cell tumors (n = 15) were negative for all markers. If T-cell and B-cell differentiation can be excluded with other markers, CD43+ is a sensitive marker for myeloid differentiation. Our results show that several markers are useful in the identification of myeloid leukemia infiltrates and in distinguishing them from lymphoblastic and lymphocytic lymphomas and small round-cell tumors in formaldehyde-fixed, paraffin-embedded tissue.