KP1 CD68 EXPRESSION IN MALIGNANT NEOPLASMS INCLUDING LYMPHOMAS, SARCOMAS, AND CARCINOMAS/

Expression of KP1/CD68 macrophage-associated antigen in a series of 84 0 selected malignant neoplasms, including immunomorphologically charac terized cases of non-Hodgkin's lymphoma (NHL) (434), Hodgkin's disease (HD) (115), soft tissue sarcoma (147), carcinoma (49), and other tumo rs (95), was examined. KP1 expression was detected in a significant nu mber of NHLs (107 of 434; 24.7%), most of them (65 of 107; 60.7%) of t he diffuse small cell subtype. Only 14 of the 155 large cell lymphomas , compared to 10 of the 51 Ki-1/CD30+ anaplastic large cell (ALC) lymp homas examined, were KP1 positive. Conversely, none of the T-lineage N HL-other than Ki-1/CD30+ ALC lymphomas-or the HD cases tested was labe led by KP1 antibody. Among the other neoplasms tested, KP1 was reactiv e with a variable proportion of cases of malignant fibrous histiocytom a (19 of 24; 79.2%), malignant schwannoma (8 of 22; 36.4%), liposarcom a (3 of 9; 33.3%), leiomyosarcoma (8 of 37; 21.6%), cutaneous or metas tatic melanoma (51 of 73; 69.9%), and renal cell carcinoma (3 of 5; 60 %). These results indicate that KP1 shows a relatively wide spectrum o f immunoreactivity with malignant neoplasms of presumed non-histiocyte origin, thus arguing against its expected specificity and high value in diagnostic pathology. Although the significance of KP1 expression b y some subsets of NHLs remains to be elucidated, its close association with B-cell NHLs, mostly of the diffuse small cell type, should stimu late further pathologic and clinical investigations.