Frequent mutation of the p53 gene in human esophageal cancer. Sequence alterations in the p53 gene have been detected in human tumors of the brain, breast, lung, and colon, and it has been proposed that p53 mutations spanning a major portion of the coding region inactivate the tumor suppressor function of this gene. To our knowledge, neither transforming mutations in oncogenes nor mutations in tumor suppressor genes have been reported in human esophageal tumors. We examined four human esophageal carcinoma cell lines and 14 human esophageal squamous cell carcinomas by polymerase chain reaction amplification and direct sequencing for the presence of p53 mutations in exons 5, 6, 7, 8, and 9. Two cell lines and five of the tumor specimens contained a mutated allele (one frameshift and six missense mutations). All missense mutations detected occurred at G.C base pairs in codons at or adjacent to mutations previously reported in other cancers. The identification of aberrant p53 gene alleles in one-third of the tumors we tested suggests that mutations at this locus are common genetic events in the pathogenesis of squamous cell carcinomas of the esophagus. 