Phorbol myristate acetate: is a tumor promoter acting as a hormone?

Tumor promoters act on carcinogen-initiated tissues to cause phenotypic expression of malignancy. Phorbol ester tumor promoters, like hormones, act on cells and tissues at nanomolar concentrations, often producing "physiological" effects. These promoters also act on cells to produce what appear to be nonphysiologic or toxic effects. One of the major questions regarding these phenomena is, Which action or actions of promoters are important in phenotypic expression of malignancy?