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Figure 2. Stage-specific roles for p21WAF1 in epithelial carcinogenesis. p21WAF1 is involved in several normal cellular processes, including cell cycle progression, cell differentiation, and senescence. p21WAF1 also has an inhibitory effect on the initiation/promotion stage(s) of carcinogenesis, thereby reducing the formation of papillomas, but does not affect conversion of these benign tumors to carcinomas. Once a carcinoma is established, however, p21WAF1 helps maintain it in a well-differentiated state, thus impeding progression to spindle cell carcinomas.
