Terminal deoxynucleotidyl transferase in non-Hodgkin's lymphoma

To investigate the specificity of terminal deoxynucleotidyl transferase (TdT) as a marker for lymphoblastic lymphoma in the non-Hodgkin's lymphomas, the authors assayed malignant cells from 142 patients with non-Hodgkin's malignant lymphoma, as well as cells from normal lymphoid tissue controls. Neoplastic cells from all 25 patients with lymphoblastic lymphoma were TdT positive. Of the remaining 117 patients with malignant lymphoma of other histologic subtypes, only one patient, with diffuse, large cell immunoblastic lymphoma, had TdT-positive cells. This patient's cells had positive results only by the enzyme assay and were TdT-negative by both immunofluorescence and immunoperoxidase assays. Of 56 patients whose cells were studied by both enzyme assay and an immunoassay method for TdT detection, a discordant result was obtained only on cells from the previously mentioned patient with large cell immunoblastic lymphoma. To determine the optimal immunoassay method, the authors studied malignant cells from 24 patients with non-Hodgkin's lymphoma for the presence of TdT by three different methods: immunofluorescence, peroxidase-antiperoxidase, and avidin-biotin-complex immunoperoxidase. Fifteen of the 24 patients had lymphoblastic lymphoma. The avidin-biotin-complex method produced superior staining, with no false-negative results. False-negative results were seen with both the immunofluorescence and peroxidase-antiperoxidase methods. Other advantages of the avidin-biotin-complex method included a marked decrease in background and non-specific staining and the ability to use higher dilutions of antisera.