p21(WAF1/CIP1) is a potent inhibitor of various cyclin-dependent kinases, the expression of which is transcriptionally regulated by tumor suppressor gene product p53. We immunohistochemically examined the expression of p53 and p21(WAF1/CIP1) in 61 esophageal squamous cell carcinomas. p53 protein was expressed in 37 (61%) of 61 carcinomas. p21(WAF1/CIP1) was consistently expressed in the normal stratified esophageal mucosa. In the carcinomas, the expression of p21(WAF1/CIP1) protein was markedly reduced or not expressed in 33 (54%) cases. Clinicopathologic analyses revealed that no significant correlation exists either between p53-positive and -negative cases or between p21(WAF1)/(CIP1)-positive and -negative cases. Twenty-four cases were p53-positive/p21(WAF1/CIP1) negative, 15 were p53-negative/p21(WAF1/CIP1)-positive, 13 were positive for both and 9 were negative for both, and these findings thus showed an inverse correlation of the positivity between p53 and p21(WAF1/CIP1) (p<0.05). Furthermore, of the 13 cases with positive staining for both, the distribution of the expression was mutually exclusive in 6 cases and coincidental in the remaining 7 cases. These findings showed the p53-dependent expression of p21(WAF1/CIP1) was observed in esophageal squamous cell carcinomas, while the lack of an absolute correlation between abnormal p53 expression and p21(WAF1/CIP1) expression suggested that the p53-independent expression of p21(WAF1/CIP1) might also occur in some portions of the esophageal squamous carcinomas, suggesting that the molecular mechanisms of esophageal carcinogenesis appear to be complicated.

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