Prior studies had indicated that stimulation of cyclic AMP signaling via Rp-mediated inhibition of PDE4 can result in growth inhibition of tumor cells of hematopoietic origin, in particular chronic lymphocytic leukemia (CLL), acute lymphocytic leukemia (ALL), and MM cells [49,50,51]. Here, PDE4A is linked to B-cell chronic lymphocytic leukemia.