PDE4A and neoplasm: Our observations that the PDE4 inhibitor, ICI 63,197, which stimulates cAMP signaling, attenuated UVB-induced apoptosis while the PDE2 inhibitor, EHNA hydrochloride, which stimulates cGMP signaling, enhanced UVB-induced apoptosis and attenuated tumor formation in a mouse model of UVB-induced carcinogenesis are partly consistent with what has been reported for intracellular cyclic nucleotides in other types of epithelial cancers.