IMMUNOHISTOCHEMICAL DETECTION OF E2F-1 IN NON-HODGKINS-LYMPHOMAS - A SURVEY OF 124 CASES

E2F-1 is a transcription factor that mediates cell cycle progression f rom the G(1) to S phase and is normally regulated by a group of protei ns, including cyclin D1, Although deregulation of E2F-1 is implicated in neoplastic transformation, in situ examination of this protein has not been performed to date. Using an immunohistochemical technique app lied to routinely fixed, paraffin-embedded tissue sections, we evaluat ed E2F-1 expression in reactive lymphoid tissues and in 124 cases of n on-Hodgkin's lymphoma (NHL) of various types. In reactive lymphoid tis sues, E2F-1 was expressed predominantly by large noncleaved cells in g erminal centers and by a small subset of cortical thymocytes. Mantle z ones and splenic marginal zones were negative. Among the NHLs, four ty pes had a relatively high percentage (> 20%) of E2F-1-positive cells: mantle cell lymphoma (19 of 19), lymphoblastic lymphoma (5 of 5), smal l noncleaved cell lymphoma (4 of 6), and hepatosplenic gamma delta T-c ell lymphoma (3 of 3). The consistent detection of many E2F-1-positive cells in mantle cell lymphoma is in contrast to other small B-cell NH Ls (n = 29), which had relatively few (< 10%) E2F-1-positive cells. Th is finding suggests that immunohistochemical staining for E2F-1 as a s upplement to the existing markers, such as cyclin D1, might be useful in the differential diagnosis of NHLs composed of small B cells.