Stains & CD markers
T cell leukemia / lymphoma protein 1 (TCL1)

Editorial Board Member: Genevieve M. Crane, M.D., Ph.D.
Editor-in-Chief: Debra L. Zynger, M.D.
Zhihong Hu, M.D., Ph.D.
Sa A. Wang, M.D.

Last author update: 19 April 2019
Last staff update: 25 January 2023

Copyright: 2019-2024,, Inc.

PubMed Search: TCL1

Zhihong Hu, M.D., Ph.D.
Sa A. Wang, M.D.
Page views in 2023: 2,484
Page views in 2024 to date: 1,294
Cite this page: Wang S, Hu Z. T cell leukemia / lymphoma protein 1 (TCL1). website. Accessed July 13th, 2024.
Definition / general
  • Locus: 14q32.13
  • Protein expression in immature T and B lymphoid cells
  • Overexpression of TCL1 is considered critical in the oncogenetic transformation (Nat Rev Cancer 2005;5:640)
Essential features
  • Other alias: T cell leukemia / lymphoma 1
Clinical features
  • T cell prolymphocytic leukemia is usually associated with inv(14)(q11;q32) or t(14;14)(q11;q32), which juxtaposes T cell leukemia 1 (TCL1) coding region with T cell receptor (TCR) locus at 14q11, resulting in overexpression of TCL1 oncoprotein (J Clin Pathol 2018;71:309)
Uses by pathologists
  • Differentiates T prolymphocytic leukemia (TCL1+) from other mature T cell lymphomas / leukemia (TCL1-) (J Clin Pathol 2018;71:309)
  • Differentiates blastic plasmacytoid dendritic cell neoplasm (TCL1+) from myeloid / monocytic sarcoma or NK cell lymphoma (TCL1-) (Blood 2003;101:5007, Mod Pathol 2014;27:1137)
  • May have prognostic significance in B cell lymphomas
Prognostic factors
  • Overexpression may be a poor prognostic factor for chronic lymphocytic leukemia and mantle cell lymphoma (Mod Pathol 2009;22:206)
  • Expression correlates with an adverse clinical outcome in diffuse large B cell lymphoma (Int J Oncol 2005;26:151)
Microscopic (histologic) images

Contributed by Zhihong Hu, M.D., Ph.D., Sa A. Wang, M.D. and Tsieh Sun, M.D.





Bone marrow aspirate





Positive staining - normal
Negative staining - normal
Negative staining - tumors
Board review style question #1
A 60 year old man presented with skin lesions and peripheral blood smear showing marked leukocytosis with lymphocytosis. The lymphocytes are small to medium with small nucleoli. Flow cytometry analysis is of peripheral blood sample shows an aberrant T cell population with the immunophenotype of
CD2+ / CD3+ / CD4+ / CD7+ / CD8+ / CD26+ / TCRa / b. Which stain would be most helpful to make a diagnosis on this patient?

  1. CD25
  2. CD30
  3. CD123
  4. TCL1
  5. TDT
Board review style answer #1
D. TCL1 stain. The major differential diagnoses include mycosis fungoides (MF) with blood involvement. Mycosis fungoides cells are more cerebriform and often show losses of CD7 and CD26 expression. Adult T cell leukemia / lymphoma often shows flower cells, with loss of CD26 and a bright expression of CD25. Peripheral T cell lymphoma with a leukemic presentation is uncommon; the immunophenotype is CD4 > CD8, with frequent CD7 loss. In the current case, the clinical presentation and immunophenotypic features of tumor cells are more in favor of T cell prolymphocytic leukemia. TCL1 protein is often overexpressed in 80 - 90% of T cell prolymphocytic leukemia, frequently due to TCL1 rearrangement as a result of inv(14)(q11;q32) or t(14;14)(q11;q32) but also can be overexpressed in the absence of the rearrangement. TCL1 is negative in mycosis fungoides, adult T cell lymphoma / leukemia and peripheral T cell lymphoma.

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Reference: T cell leukemia / lymphoma protein 1 (TCL1)
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