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]. Here, CD38 is linked to acute myeloid leukemia.