Expression of the Diffuse B-Cell Lymphoma Family Molecule Swap-70 in Human B-Cell Neoplasms - Immunohistochemical Study of 86 Cases

SWAP-70 is a recently discovered member of the Dbl (diffuse B-cell lymphoma) family of signal transduction molecules that is abundantly expressed in B cells. SWAP-70 mediates lipid second-messenger signals to the cytoskeletal-organizing GTPase Rac, functioning as a guanine-nucleotide exchange factor. SWAP-70 is strongly expressed in germinal center B cells, with low-level expression in resting B-cells. Expression of SWAP-70 in neoplastic B cells has not been described. We report the immunohistochemical expression of SWAP-70 in 86 B-cell neoplasms. SWAP-70 was strongly expressed in 59 of the 86 cases: 2 of 10 (20%) precursor B-cell lymphoblastic leukemias, 2 of 2 (100%) precursor B-cell lymphoblastic lymphomas, 2 of 4 (50%) mantle cell lymphomas, 7 of 9 (78%) Burkitt lymphomas, 9 of 9 (100%) diffuse large B-cell lymphomas, 8 of 8 (100%) follicular lymphomas, 6 of 6 (100%) nodular lymphocyte predominant Hodgkin lymphomas, 0 of 8 (0%) classic Hodgkin lymphomas, 12 of 13 (92%) chronic lymphocytic leukemias, 3 of 3 (100%) nodal marginal zone lymphomas, 5 of 5 (100%) extranodal marginal zone lymphomas, 1 of 2 (50%) splenic marginal zone lymphomas, 2 of 3 (66%) hairy cell leukemias, and 0 of 4 (0%) plasma cell neoplasms. All 4 T-cell lymphomas were nonreactive for SWAP-70: 0 of 3 peripheral T-cell lymphomas and 0 of 1 anaplastic large cell lymphoma. These results suggest that a spectrum of neoplastic B cells maintains activation of this signal transduction pathway. This is the first report of the expression of a Dbl family molecule in human lymphoma and leukemia tissues.