CD5 labeling of thymic carcinomas and other nonlymphoid neoplasms

We studied 109 thymic tumors and 423 other neoplasms for immunocytochemical expression of CD5 in paraffin-embedded tissue using 2 monoclonal antibodies. One of the antibodies (clone CD5/54/B4) labeled 7 (29%) of 24 thymic carcinomas but did not stain any of the other neoplasms. In contrast, the other antibody (clone 4C7) labeled 15 (62%) of 24 thymic 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 peripheral T-cell lymphomas and 1 of 4 anaplastic large cell lymphomas. Clone 4C7 produced strong labeling of reactive T lymphocytes, whereas CD5/54/B4 staining of these cells was weak or absent. No other normal cells seemed to stain with either antibody. In conclusion, one CD5 antibody clone (CD5/54/B4) specifically identified 30% of thymic carcinomas. The other CD5 antibody (clone 4C7) identified 62% of thymic carcinomas but also labeled occasional other neoplasms.