RB1 and neoplasm: The comparative analysis of tumor appearance in Trp53ΔEC and RbΔEC; Trp53ΔEC mice have revealed an accelerated tumor onset in RbΔEC; Trp53ΔEC indicating the existence of cooperative functions for these tumor suppressors in epidermis, which is in contrast with the absence of spontaneous tumors [17] and the reduced susceptibility to chemical carcinogenesis in mice lacking epidermal pRb [18].