OBJECTIVE p53 is the most commonly mutated gene in human cancers. The objective of this study was to determine if clear cell adenocarcinomas (CCAs) of the vagina and cervix are associated with p53 gene mutations or alterations in p53 tumor-suppressor protein expression. METHODS Paraffin-embedded tissue specimens from 21 women (median age 22 years) with clear cell adenocarcinoma of the vagina or cervix were studied. Fifteen women had a prior history of in utero exposure to diethylstilbestrol. p53 protein expression was detected by immunohistochemical (IHC) analysis with monoclonal antibody DO-7 (Dako Corp.) which recognizes both wild-type and mutant p53 proteins. For p53 gene analysis, genomic DNA from malignant tissue was isolated and exons 4-10 were amplified by PCR and subjected to mutation screening by single-stranded conformation polymorphism (SSCP) analysis. RESULTS p53 protein was detected by IHC in tumors from 14 of 21 cases (67%). The observed p53 staining patterns were heterogeneous in both the proportion and intensity of tumor cells stained but were clearly overexpressed relative to the surrounding benign stroma. Metastatic tumors from 3 women with metastatic disease were also positive for p53 staining. SSCP analysis did not identify p53 mutations in any of the cases and strongly suggests that the tumors contained only wild-type p53 alleles. CONCLUSIONS Recent studies have demonstrated that wild-type p53 may accumulate in response to DNA damage which normally leads to growth arrest or programmed cell death. Our observations are consistent with the hypothesis that p53 overexpression in CCAs of the vagina and cervix is a response to generalized DNA damage, rather than a result of p53 protein half-life prolongation resulting from mutational inactivation of p53. Overexpression of wild-type p53 protein in vaginal and cervical CCA may relate to the more favorable prognosis of this subset of tumors in comparison to other gynecologic tumors containing mutated p53 genes.