CD5 LABELING OF THYMIC CARCINOMAS AND OTHER NONLYMPHOID NEOPLASMS

We studied 109 thymic tumors and 423 other neoplasms for immunocytoche mical expression of CD5 in paraffin-embedded tissue using 2 monoclonal antibodies. One of the antibodies (clone CD5/54/B4) labeled 7 (29%) o f 24 thymic carcinomas but did not stain any of the other neoplasms. I n contrast, the other antibody (clone 4C7) labeled 15 (62%) of 24 thym ic carcinomas, 2 (2%) of 84 thymomas, 3 (8%) of 37 lymphomas, and 14 ( 4%) of 386 other tumors. Among the lymphomas, 4C7 labeled 2 of 4 perip heral T-cell lymphomas and 1 of 4 anaplastic large cell lymphomas. Clo ne 4C7 produced strong labeling of reactive T lymphocytes, whereas CD5 /54/B4 staining of these cells was weak or absent. No other normal cel ls seemed to stain with either antibody. In conclusion, one CD5 antibo dy clone (CD5/54/B4) specifically identified 30% of thymic carcinomas. The other CD5 antibody (clone 4C7) identified 62% of thymic carcinoma s but also labeled occasional other neoplasms.