Stains & CD markers
TdT


Last author update: 21 July 2022
Last staff update: 21 July 2022

Copyright: 2003-2022, PathologyOutlines.com, Inc.

PubMed Search: TdT

Austin Ellis, M.D.
Ling Zhang, M.D.
Page views in 2021: 11,328
Page views in 2022 to date: 6,682
Cite this page: Ellis A, Zhang L. TdT. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/stainstdt.html. Accessed August 17th, 2022.
Definition / general
Essential features
  • Nuclear marker expressed in most precursor lymphoid neoplasms
  • Expressed in the variable number of nonneoplastic immature T lymphocytes (thymocytes) in thymoma; however, some cases lack clusters of thymocytes
  • Expressed in many cases of Merkel cell carcinoma and blastic plasmacytoid dendritic cell neoplasm, which may be a diagnostic pitfall
  • Expressed in approximately 10% of acute myeloid leukemia (that is, not lineage defining)
  • Not expressed in mature B cell neoplasms that may have blastoid morphology, such as mantle cell lymphoma or high grade B cell lymphoma
  • Not expressed in Ewing sarcoma
Terminology
  • DNA nucleotidylexotransferase (DNTT)
  • Terminal deoxynucleotidyl transferase (TdT)
Pathophysiology
  • Catalyzes addition of deoxynucleotides to the 3'-OH end of DNA primers
  • Adds nontemplated nucleotides at the junctions of V(D)J gene segments (Chembiochem 2019;20:860)
  • Contributes to immunoglobulin and T cell receptor diversity
Interpretation
  • Nuclear stain
Uses by pathologists
  • Differentiating precursor lymphoid neoplasms, which may not express CD45, from other small blue cell tumors
  • Identifying clusters of thymocytes in thymoma, which are typically absent in thymic carcinoma
Prognostic factors
  • B lymphoblastic leukemia / lymphoma that does not express TdT may be associated with KMT2A rearrangements and lower 5 year event free survival (Mod Pathol 2021;34:2050)
  • TdT expression in acute myeloid leukemia with an intermediate risk karyotype may be associated with increased risk of relapse (Int J Hematol 2020;112:17)
  • TdT expression in Merkel cell carcinoma may be associated with improved overall survival (Am J Clin Pathol 2020;154:38)
Microscopic (histologic) images

Contributed by Austin Ellis, M.D.
B lymphoblastic leukemia / lymphoma B lymphoblastic leukemia / lymphoma

B lymphoblastic leukemia / lymphoma

B lymphoblastic leukemia / lymphoma PAX5 B lymphoblastic leukemia / lymphoma TdT

B lymphoblastic leukemia / lymphoma

T lymphoblastic lymphoma T lymphoblastic lymphoma

T lymphoblastic lymphoma



Contributed by Renuka Agrawal, M.D. (Case #126)
Pre B lymphoblastic lymphoma

Pre-B lymphoblastic lymphoma

Virtual slides

Images hosted on other servers:
Mixed phenotype acute leukemia, H&E Mixed phenotype acute leukemia, TdT

Mixed phenotype acute leukemia

Positive staining - normal
Positive staining - disease
Negative staining
Sample pathology report
  • Mediastinal mass, needle core biopsy:
    • T lymphoblastic leukemia / lymphoma (see comment)
    • Comment: The needle core biopsy demonstrates sheets of intermediate size lymphoid cells with somewhat irregular nuclear contours, finely stippled chromatin and scant cytoplasm. Scattered tingible body macrophages are present. The neoplastic cells are positive for CD3 (cytoplasmic), CD5, CD7, CD4, CD8, CD10 and TdT and negative for CD30 and ALK1. Ki67 is 95%.
Board review style question #1

A 19 year old man presents with respiratory distress. Computed tomography (CT) of his chest identifies a mass in the anterior mediastinum. Core biopsy of the mass consists of sheets of intermediate size cells with finely stippled chromatin and scant cytoplasm. The cells are negative for CD45 and positive for CD99 and TdT. Cytokeratin AE1 / AE3 is negative. Scattered tingible body macrophages are present. Which of the following is true regarding the lesional cells?

  1. TdT expression indicates they are derived from precursor lymphoid cells
  2. TdT expression precludes a diagnosis of thymic hyperplasia
  3. TdT expression supports a diagnosis of Ewing sarcoma
  4. TdT expression supports a diagnosis of neuroblastoma
Board review style answer #1
A. TdT expression indicates they are derived from precursor lymphoid cells

Comment Here

Reference: TdT
Back to top
Image 01 Image 02