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Absence of CD26 Expression Is a Useful Marker for Diagnosis of T-Cell Lymphoma in Peripheral Blood

Dan Jones MD, PhD, Nam H. Dang MD, PhD, Madeleine Duvic MD, LaBaron T. Washington MD, Yang O. Huh MD
DOI: http://dx.doi.org/10.1309/U1Y6-J4AG-5M4M-7AYV 885-892 First published online: 1 June 2001


We report flow cytometric characterization of surface CD26 expression in 271 peripheral blood samples from 154 patients evaluated for the presence of a T-cell lymphoproliferative disorder, primarily mycosis fungoides/Sézary syndrome (MF/SS). The presence of morphologically identifiable tumor cells on peripheral blood smears was the criterion for lymphomatous involvement. In 66 of 69 samples from 28 patients, we identified an abnormal CD26–/dim T-cell population that was distinct from the variable CD26 expression seen in normal peripheral blood T cells. This population was CD26– in 23 patients and weakly CD26 + in 5 patients. CD7 was more variably expressed in MF/SS tumor cells, allowing recognition of a distinct, quantifiable abnormal T-cell population in only 34 of 69 involved samples. An increased CD4/CD8 ratio and lower surface expression of CD4 in tumor cells also helped separate the CD26–/dim atypical population for quantification. In 35 blood samples from other types of T-cell tumors, tumor cells in 10 of 11 morphologically involved cases showed absent/dim CD26. Although capable of detecting abnormalities in most cases of MF/SS, CD7 expression does not provide as clear a separation of the neoplastic population and can be replaced by CD26 staining in routine peripheral blood flow cytometric screening of MF/SS patients.

Key Words:
  • Mycosis fungoides
  • Flow cytometry
  • T-cell lymphoma
  • Tumor markers