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

  1. Dan Jones, MD, PhD1,
  2. Nam H. Dang, MD, PhD2,
  3. Madeleine Duvic, MD3,
  4. LaBaron T. Washington, MD1, and
  5. Yang O. Huh, MD1
  1. 1From the Division of Pathology and Laboratory Medicine and the Departments of
  2. 2Lymphoma and
  3. 3Dermatology, the University of Texas–M.D. Anderson Cancer Center, Houston


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.


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