The diagnosis of primitive
hematologic malignancies in extramedullary sites (
lymphoblastic lymphoma of T- or B-cell type and
myeloid sarcoma) on
paraffin-embedded tissue sections is difficult and often impossible because of the primitive morphology of the neoplastic cells. The authors studied 21 extramedullary
tumors of lymphoid or myeloid blasts. They used a panel of 22
antibodies on frozen sections and 9
antibodies on
paraffin sections to determine the spectrum of immunophenotypes and to develop a practical panel for diagnosis. All but two of the cases could be classified as lymphoid or myeloid using immunohistologic analysis. Thirteen cases were classified as
lymphoblastic lymphoma/
acute lymphoblastic leukemia (LBL/ALL); 10 were classified as precursor T (CD7+, CD3+/-, CD45+) and 3 as precursor B-cell (CD19+/-CD10+CD45-) type. Five cases were classified as
myeloid sarcoma (CD13+
myeloperoxidase+,
lysozyme+). Two LBL/ALL coexpressed either CD33 (1 case) or CD15 (1 case), and one
myeloid sarcoma coexpressed TdT and CD7. One case appeared to be truly mixed lineage, coexpressing CD3 with
myeloperoxidase and
lysozyme, and two cases expressed no lineage-specific
antigens. There were clinical differences between the three major
tumor types, and within the category of T-precursor LBL/ALL, classification according to stage of thymocyte differentiation was associated with distinctive clinical features. In conclusion, the spectrum of immunophenotypes detected on frozen section was similar to that reported by flow cytometry on peripheral blood and bone marrow specimens. The most useful
antigens on frozen sections were CD7 and CD3 (T cell), CD10 and CD19 (B cell), and CD13 (myeloid). TdT was coexpressed by one
myeloid sarcoma and was undetectable in 40% of LBL/ALL. On
paraffin sections,
myeloperoxidase and
lysozyme were reliable markers of myeloid lineage, but none of the markers used on
paraffin sections distinguished between LBL/ALL of T- and B-precursor types. Both B-LBL/ALL and
myeloid sarcomas were often CD45- on
paraffin sections, which may be a obstacle in determining the diagnosis. These distinctions appear to have clinical relevance.