Cell proliferation assays showed that there was no significant difference in the proliferative capacity of CD9+ cells and CD9− cells from either THP-1 cells or AML patients (Fig. 2a, b, p = 0.9669 and p = 0.9005, respectively), which is consistent with previous reports that stem cells do not exhibit superior proliferation capacity under normal conditions [39–41]. This evidence concerns the gene CD9 and acute myeloid leukemia.