OBJECTIVE To determine whether mutation in the DNA of the estrogen-receptor gene occurs in endometrial cancer. METHODS Polymerase chain reaction amplification and single-stranded conformation polymorphism analysis of the entire coding region (exons 1-8) of the human estrogen-receptor gene, as well as an untranslated region (exon I*) in the gene, were performed on genomic DNA extracted from 56 snap-frozen endometrial cancers. All cancers demonstrating mobility shifts on single-stranded conformation polymorphism suggestive of DNA sequence alteration were subjected to definitive DNA sequencing of the relevant portion of the estrogen-receptor gene. RESULTS In addition to detecting a frequent, previously described polymorphism in exon 1, single-stranded conformation polymorphism analysis of the 56 endometrial cancers identified seven cancers with mobility shifts. Three cancers shifted in exon 3, one cancer each shifted in exons 4 and 7, and two shifted in exon 8. Deoxyribonucleic acid sequencing revealed sequence alterations in all seven cases demonstrating mobility shifts. In six of these seven cases, these alterations were consistent with infrequent silent polymorphisms; in the seventh cancer, the sequence alteration proved to be a somatic missense mutation at codon 537 in the region of the estrogen-receptor gene encoding the hormone-binding domain of the receptor protein. CONCLUSIONS The infrequent DNA mutation in the estrogen-receptor gene is unlikely to account for the variation in estrogen-receptor expression observed in endometrial cancer.