Considering that the main mechanism of the anticancer action of triterpenoids is most often associated with the activation of apoptosis in cancer cells [12,14], the possibility of OA inducing apoptotic cell death in adherent HBL-100 and suspension K562 cells and their resistant subclones HBL-100/Dox and K562/iS9 was further analyzed via flow cytometry using Annexin V-FITC/PI double staining (Figure 6 and Figure S1). The gene discussed is ANXA5; the disease is cancer.