To study whether valproate could induce CD20 expression in patient del13q/NOTCH1wt CLL cells, and to ascertain that valproate treatment at a clinically relevant dose could result in HDAC inhibition, untreated leukemic cells from patient 1, 2 and 4 were incubated with 1000 μM of valproate in vitro. The gene discussed is HDAC9; the disease is B-cell chronic lymphocytic leukemia.