PCBs. LW Robertson and LG Handsen, eds., Lexington, KY: The University of Kentucky Press, 2001 Jan; :373-379
Progression is the conversion of initiated and promoted cells into cancer cells. This stage of neoplasia is characterized by an increased growth rate, metastasis, aneuploidy and evolving karyoptic instability. The stage of progression has been examined in experimental models of skin and liver cancer. Early experiments of multistage epidermal carcinogenesis demonstrated that neoplasms occur at a high frequency when complete carcinogens are applied chronically (Shubik et al., 1950). In the skin model, it was demonstrated that chronic application of an initiator to mouse skin shortened the latency to neoplasia (Roe et al., 1972; Hennings, et al., 1985). The stage of progression in liver cancer has been examined by an initiation-promotion-initiation protocol (IPI) that was first suggested by Potter (1981) and later demonstrated experimentally by Scherer (1984). In the rat liver model, the transition from preneoplastic to tumor is characterized by the appearance of foci in foci, increated chromosome damage (Pitot et al., 1989, Pitot, et al., 1991; Dragan et al., 1993; Sargent et al., 1996), and increased incidence of carcinomas (Scherer, et al., 1984; Reddy, et al., 1982).
Dr. Linda M. Sargent, NIOSH, MS-3014, 1095 Willowdale Road, Morgantown, WV 26505, USA