[1590] Evaluation of Tonsillectomy Specimens for Terminal Deoxynucleotidyl Transferase (TdT) Expression by Immunohistochemistry

John Wayne, Jerry W Hussong, Randa Alsabeh. Cedars-Sinai Medical Center, Los Angeles, CA

Background: Terminal deoxynucleotidyl transferase (TdT) is a specialized DNA polymerase expressed in thymic tissue, hematogones, acute lymphoblastic leukemia/lymphomas and a small subset of acute myeloid leukemias. The expression of TdT has been previously studied in children tonsils. The aim of this study is to investigate TdT expression in tonsils by age distribution.
Design: 60 benign tonsillectomy specimens were retrospectively reviewed. They were from patients of both sexes from 1 year to 69 years. A panel of immunohistochemical stains including TdT, CD10, CD34, CD3, CD20, PAX-5, and CD79a were performed. Evaluation of the distribution pattern of TdT staining was performed. Quantification of the number of TdT positive cells in the 40X field with the highest number of TdT positive cells was recorded. A tonsil was considered positive for TdT if at least one well defined nucleus was positive for TdT by immunohistochemical staining.
Results: There were 32 females and 28 males. Overall, 59 of 60 tonsils had TdT positive cells. Overall, the average number of TdT positive cells per high power field in the areas of highest expression was 61 with a range of 0-573 positive cells per high power field. The average number of TdT positive cells per high power field in the areas of highest expression was 123 (9-573) for 1-10 years old, 70 (1-260) for 11-20 years old, 35 (2-83) for 21-30 years old, 32 (1-63) for 31-40 years old, 36 (0-115) for 41-50 years old, 32 (2-88) for 51-60 years old, and 9 (1-17) for 60-69 years old. The TdT positive cells were found primarily in the fibrous septal bands of the tonsil. None of the Tdt positive cells expressed CD3 or CD79a using dual expression staining. No CD34 positive cells were identified.
Conclusions: TdT is a useful marker of immaturity in lymphoid cells as well as in the diagnosis of lymphomas and leukemias. Variable numbers of TdT positive cells, however, can be identified in non-neoplastic tonsils. These cells do not appear to express T or B-cell lineage markers such as CD3 or CD79a. A greater number of TdT positive cells were seen in patients less than 21 years of age. Identification of isolated TdT positive cells in tonsillar specimens does not equate to malignancy and should not be used as a primary determinant in the diagnosis of lymphoma or leukemia in these specimens.
Category: Hematopathology

Wednesday, March 21, 2012 1:00 PM

Poster Session VI # 238, Wednesday Afternoon


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