Flow Cytometry Assessment of CD26+ Leukemic Stem Cells in Chronic Myeloid Leukemia.

UNLABELLED: Flow cytometry based assessment of CD26+ leukemic stem cells (LSCs), a recently described diagnostic marker, has emerged as a promising tool for diagnosis of chronic myeloid leukemia (CML). In this prospective observational study, peripheral blood samples from suspected CML patients were evaluated by flow cytometry to assess the expression of CD26 on stem cell compartment (CD45+CD34+CD38-).Molecular confirmation of diagnosis was done by RT-PCR for BCR::ABL1 transcript. Patients initiated on tyrosine kinase inhibitors(TKIs) were followed upto twelve months to evaluate the kinetics of CD26+ LSCs. Out of the eighty six cases enrolled, CD26 expression was detectable in seventy five cases. All these seventy five cases were confirmed positive for BCR::ABL1 transcript by RT-qPCR. Eleven cases lacking CD26 expression were uniformally negative for BCR::ABL1.There was no significant correlation of the CD26 levels with age, sex, percentage of blasts, total leucocyte count, basophils, Sokal score or ELTS score. At twelve months, seven patients achieved major molecular response; of these two became negative for CD26+ LSCs, while five demonstrated a non significant decline. Flow cytometric assessment of CD26+ LSCs is a rapid, cost effective and robust diagnostic tool for diagnosis of CML. Monitoring CD26+ LSC kinetics during TKI therapy may provide a surrogate marker for monitoring response, warranting validation in larger cohorts. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at https://doi.org/10.1007/s12288-025-02182-w.