For AML, it was previously hypothesized that ALDH enzymatic activity marks a positive outcome because a drop in activity was found in cancer patients when compared to that of healthy study volunteers; yet, soon after, in addition to identifying nonmalignant stem cells within some AML samples, high-level ALDH activity was also a marker of CD34+/CD38− leukemic stem cells in some patients [29,30,31,32,33]. The gene discussed is CD34; the disease is acute myeloid leukemia.