Given that OPN has various isoforms in bone marrow, we tested the adhesion of leukaemia cells to thrombin-cleaved OPN, which is the most dominant form of OPN in bone marrow.9 Similar to a previous study,10 leukaemia cells only weakly adhered to full-length OPN but they showed strong adhesion to thrombin-cleaved OPN (Supplementary figure 1c). This evidence concerns the gene SPP1 and leukemia.