To investigate the dynamics of leukemic HSPC subpopulations during AML development, their genetic composition and leukemogenic potential at diagnosis and relapse were evaluated in samples derived from 15 patients, who expressed high levels of CD34+/CD38− in the blast fraction, as these primitive leukemic stem cells are considered markers for poor prognosis due to high relapse risk [10,22]. The gene discussed is CD38; the disease is acute myeloid leukemia.