PDCD4 and papilloma: Loss of Pdcd4 enhances neoplastic transformation, activator protein 1 (AP-1) transactivation, intravasation, and invasion in vitro [3,4] and Pdcd4-deficient mice appear more susceptible to the two stage skin carcinogenesis model, whereas transgenic overexpression of Pdcd4 decreased papilloma incidence and multiplicity in this model [5,6].