Distinction between undifferentiated (small noncleaved) and lymphoblastic lymphoma. An immunohistologic study on paraffin-embedded, fixed tissue sections.

The morphologic differentiation between malignant lymphoma of the small noncleaved cell (SNC) type and lymphoblastic lymphoma (LBL) is at times difficult, particularly when fresh tissue is not available for immunologic studies. We have examined the reactivities of a panel of monoclonal and polyclonal antibodies, including LN-1, LN-2, and antibodies to immunoglobulin light chains, leukocyte common antigen (LCA), Leu-M1, vimentin, S-100 protein, lysozyme, and alpha-1-antitrypsin, in paraffin-embedded, B5- and formalin-fixed tissue involved by SNC or LBL. The immunophenotypes in all of the cases included in this study had been characterized previously in fresh-frozen sections or cell suspensions. Among 21 samples of B5-fixed SNC, LN-1 was reactive in 17 and LN-2 in 18 cases. Among 13 B5-fixed LBL, LN-1 was reactive in two cases and LN-2 was reactive in two cases. Each of 20 B5-fixed samples of SNC was reactive with at least one of the antibodies, whereas 10 of the 13 B5-fixed samples of LBL were negative for both antibodies. Lesser reactivity was evident in formalin-fixed tissues, with only nine of 27 SNC specimens positive for LN-1 and 16 of 27 positive for LN-2. Most or all of the SNC and LBL samples were negative for immunoglobulin light chains, Leu-M1, vimentin, S-100 protein, lysozyme, and alpha-1-antitrypsin. The majority of both SNC and LBL were positive for LCA. We conclude that LN-1, preferably in combination with LN-2, can be used for distinguishing between SNC and LBL in paraffin-embedded, B5-fixed tissue when fresh tissue is not available.