Stage of Tumor Progression,Progressor Agents,and Human Risk

Abstract

Abstract

That cancer develops from an antecedent process consisting of distinct, definable stages or phases is now considered to be the case in the development of the majority of animal and human neoplasms (1-5). In some of the earliest studies in experimental animals demonstrating the existence of such stages (6-8), two stages, termed initiation and promotion, occurred in that order preceding the development of tumors. The majority of tumors occurrin in the system studied, that of mouse epidermal carcinogenesis, were benign papillomas, and carcinomas developed only later. Subsequently, Foulds (9), from studies on experimental mammary adenocarcinoma, argued that the stage following initiation be termed “progression”, to represent a continuous spectrum of alterations, presumably irreversible, beginning with the initiated cell.