A measurement in which the number of individuals in a study population that display one or more prostate tumorous lesion(s) at a point in time or develop such lesions within a determined period of time are compared to the total number of individuals in the study population. Often expressed as a percentage but could be expressed as a ratio. A tumorous lesion is one which is or has the potential to become a tumor, that is, a neoplasm or new growth of tissue in which cell multiplication is more or less uncontrolled and progressive. Tumorous lesions include tumors, preneoplastic lesions, and hyperplastic lesions composed of histologically normal cells.