Leu-M1 immunoreactivity in nonhematopoietic neoplasms and myeloproliferative disorders. An immunoperoxidase study of paraffin sections.

Leu-M1 is a differentiation antigen present on human myelomonocytic cells, which also has been identified in Reed-Sternberg cells and variants of Hodgkin's disease. This study further defines the tissue distribution of Leu-M1, with immunoreactivity observed for neoplastic cells in 14 of 28 formalin-fixed, paraffin-embedded nonhematopoietic neoplasms. With the use of monoclonal antibodies and an indirect immunoperoxidase technic, Leu-M1 was detected in adenocarcinomas of various sites (breast, lung, colon, thyroid, pancreas, and stomach), in squamous cell and transitional cell carcinomas, and in a small-cell anaplastic carcinoma. Evaluation of a wide variety of myeloproliferative disorders indicated that Leu-M1 effectively characterized mature and immature monocytic cells and myeloid cells at late stages of granulopoiesis, but it was not a reliable marker for early myeloid cells including blasts. Leu-M1 monoclonal antibodies are a useful diagnostic reagent, particularly in the assessment of lymphoproliferative disorders, but must be used with extreme caution and full awareness of its staining profile.