FREQUENT MUTATIONS OF P53 GENE IN ESOPHAGEAL SQUAMOUS-CELL CARCINOMASWITH AND WITHOUT HUMAN PAPILLOMAVIRUS (HPV) INVOLVEMENT SUGGEST THE DOMINANT ROLE OF ENVIRONMENTAL CARCINOGENS IN ESOPHAGEAL CARCINOGENESIS

Epidemiological evidence suggests that alcohol intake, use of tobacco, ingestion of mycotoxins and nitrosamines and nutritional deficiencies are high-risk factors for the development of oesophageal cancer. Simi larly, viral infections have been postulated to play a role in some tu mours. However, the molecular events underlying the development of oes ophageal carcinoma are poorly understood as yet. Loss of p53 tumour-su ppressor gene function has been found in different human malignancies, and it can occur in a variety of ways, including gene mutation and in teraction with the E6 protein of oncogenic human papillomaviruses (HPV s). Because the oesophageal mucosa is potentially exposed to mutagens and HPVs, we studied DNA samples derived from nine HPV-positive squamo us cell carcinomas and 12 HPV-negative tumours. Exons 5-9 of the p53 g ene containing phylogenetically conserved domains were examined using the polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) technique. HPV detection was done using DNA in situ hybridi sation with biotin-labelled HPV DNA probes. Mutations were detected in eight (38%) out of the 21 cases. Three mutations were found in exons 5/6, three in exon 7 and two in exon 8/9. Six (50%) of the 12 HPV-nega tive carcinomas showed p53 mutations. Two (22.2%) of the nine HPV-posi tive carcinomas were found to contain p53 mutations as well; one conta ined HPV 16 DNA sequences and showed p53 mutation in exon 8/9, and the other was HPV 6/11 positive with the mutation in exon 5/6. Although m utations were more common in HPV-negative tumours (50.0% vs 22.2%), th e difference in p53 mutations in HPV-positive and -negative tumours di d not reach statistical significance (P=0.1946). These data indicate t hat inactivation of the p53 gene is a frequent event in oesophageal sq uamous cell carcinomas and such an inactivation might be an important molecular pathway for the development of oesophageal cancer. The findi ngs of p53 mutations in HPV-positive oesophageal carcinomas suggest th at HPV and p53 mutation were not mutually exclusive events. The presen ce of frequent mutations of p53 gene in both HPV-positive and -negativ e oesophageal carcinomas suggests a dominant role of environmental car cinogens in oesophageal carcinogenesis.