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Flow Cytometry in the Differential Diagnosis of Lymphocyte-Rich Thymoma From Precursor T-Cell Acute Lymphoblastic Leukemia/Lymphoblastic Lymphoma

Shiyong Li MD, PhD, Jonathan Juco MD, Karen P. Mann MD, PhD, Jeannine T. Holden MD
DOI: http://dx.doi.org/10.1309/K2FY1TED8GEGFLNG 268-274 First published online: 1 February 2004


We compared the antigen expression profile of thymocytes in lymphocyte-rich thymoma with that of precursor T-cell acute lymphoblastic leukemia/ lymphoblastic lymphoma (T-cell ALL/LBL) cells using 4-color flow cytometry. In all 15 thymoma cases, the thymocytes demonstrated 3 distinct subpopulations. The least mature cells (double-negative) expressed low-density CD2 and CD5, high-density CD7, CD10, CD34, and heterogeneous CD4 and CD8. They had the lowest density CD45 expression and were surface CD3–. The immature cells (double-positive) expressed CD2, CD5, CD7, CD4, CD8, heterogeneous surface CD3, and intermediate-density CD45. They were CD10– and CD34–. The mature cells (single-positive) expressed CD2, surface CD3, CD5, CD7, and CD4 or CD8. The heterogeneous expression of surface CD3, CD4, and CD8 also created a characteristic smearing pattern for these antigens. In all 15 T-cell ALL/LBL cases, the lymphoblasts formed a tight cluster without discrete subpopulations or smearing pattern. Of 5 double-negative cases, 4 demonstrated loss of CD2, CD10, or CD34 expression. Of 7 double-positive cases, 5 showed complete loss of surface CD3, CD2, and/or CD5; 4 were CD10+; and 2 were CD34+. Of 3 single-positive cases, 2 showed loss of CD2 and/or aberrant expression of CD34. Analysis of antigen expression pattern, the presence or absence of T cell–associated antigen deletion, and the expression of CD10 and CD34 by 4-color flow cytometry can help differentiate thymoma from T-cell ALL/LBL.

Key Words:
  • Thymoma
  • Precursor T-cell acute lymphoblastic leukemia
  • T-cell lymphoblastic lymphoma
  • Flow cytometric immunophenotyping