To validate CML specificity of PB CD26+ LSCs detected during TKI treatment and to confirm that also circulating CD26+ LSCs are Philadelphia-positive, we performed dual fusion BCR-ABL1 FISH analysis of PB sorted CD34+/CD38−/CD26+ in five CML patients at 3–6 months after starting TKI treatment. The gene discussed is ABL1; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.