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Esophageal tissue sections stained with proliferating cell nuclear antigen (PCNA). (A) Low-level PCNA staining in normal esophageal epithelium; (B) increased PCNA nuclear reactivity in dysplastic esophageal epithelium; (C) intense PCNA staining in N-nitrosomethylbenzylamine–induced papilloma tissue at Week 26; and (D) positive staining in rat colon control tissue.
