Impaired phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA)-mediated proliferation was seen in the AQP3-deficient epidermis during the tumor promotion step, and the author postulated that this is due to the lack of promotion of the initiated cells, resulting in the absence of papillomas (91). The gene discussed is AQP3; the disease is neoplasm.