Stains - TdT

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Stains

TdT

Reviewer: Nat Pernick, M.D. (see Reviewers page)
Revised: 25 February 2012, last major update February 2012
Copyright: (c) 2002-2012, PathologyOutlines.com, Inc.

Definition
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● Terminal deoxynucleotidyl transferase; also called terminal transferase
● Nuclear DNA polymerase in thymic and small number of bone marrow cortical lymphocytes
● Catalyzes addition of deoxynucleotides to 3' OH ends of oligonucleotides or polydeoxynucleotides
● Performs DNA synthesis using only single-stranded DNA as the nucleic acid substrate (Biochim Biophys Acta 2010;1804:1151)
● Used during immunoglobulin and T cell receptor rearrangement, adds diversity to antibody recognition sites
● Absent in fetal liver hematopoietic stem cells, which impairs junctional diversity in B cells during the fetal period

Uses by pathologists
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● Interpretation: nuclear stain
● Marker of B or T cell acute lymphoblastic leukemia/lymphoma (only rarely negative, Arch Pathol Lab Med 2000;124:92)

Micro images
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Bone marrow: hematogones with coarsely granular or speckled pattern of terminal deoxynucleotidyl transferase (TdT) immunofluorescence, which often intensely aligns the nuclear membrane (green)


Bone marrow: acute myeloid leukemia (left) and recursor B-lymphoblastic leukemia (right) with a finely granular pattern of terminal deoxynucleotidyl transferase (TdT) immunofluorescence, which is uniformly distributed in the nucleus (green)


pre-B lymphoblastic lymphoma of kidney (left), skin (right)

Lymphoblastic lymphoma with basal cell carcinoma


Merkel cell carcinoma

Positive staining - normal
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● Hematogones (B and T cell precursors, coarsely granular or speckled pattern of TdT immunofluorescence, which often intensely aligns the nuclear membrane, Am J Clin Pathol 2008;129:700), cortical thymocytes
● Note: TdT+ lymphoid precursors are present in benign pediatric lymph nodes (Am J Clin Pathol 2002;118:248) and tonsils (Am J Clin Pathol 2001;116:12), causing possible confusion in ALL patients

Positive staining - disease
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● Acute lymphoblastic lymphoma: 95%, diffuse and strong, finely granular pattern of TdT immunofluorescence uniformly distributed in the nucleus
● Acute myelogenous leukemia / myeloid sarcoma: variable, often weak and focal
● Blastic plasmacytoid dendritic cell neoplasm: 60% (Am J Surg Pathol 2010;34:75)
● Indolent T cell proliferations
● Merkel cell carcinoma: >50% (Mod Pathol 2007;20:1113, Am J Clin Pathol 2011;135:831)
● Thymoma-lymphocyte predominant

Negative staining
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● Myeloid cells; mature leukemias/lymphomas including Burkitt, diffuse large B cell, MALT, mantle cell, prolymphocytic leukemia (T cell)
● Small cell lung carcinoma (usually); sarcomas

End of Stains > TdT

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