High prevalence of K-ras-2 mutations in hepatocellular carcinomas in workers exposed to vinyl chloride

Objectives: Vinyl chloride (VC) and its metabolites are human carcinogens a ssociated with liver angiosarcomas (LAS) and also with hepatocellular carci nomas (HCCs). In VC associated LAS mutations of the K-ras-2 gene have been reported; however, no data about the prevalence of such mutations in VC-ass ociated HCCs are available. The aim of the study was to evaluate possible s pecific K-ras-2 oncogene mutations in the case of HCCs due to VC. Methods: The presence of K-ras-2 mutations was analysed in tissue from 12 patients w ith VC-associated HCCs. All patients had known longterm exposure to VC (ave rage exposure amount: 9,942 ppm-years). Twenty patients with hepatocellular carcinoma due to hepatitis B (n = 7), hepatitis C (n = 5) and alcoholic li ver cirrhosis (n = 8) served as a control group. The specific mutations wer e determined by direct sequencing of codons 12 and 13 of the K-ras-2 gene i n carcinomatous and adjacent non-neoplastic liver tissue after microdissect ion. Immunohistochemical analysis was performed to detect p21(ras) protein. Results: K-ras-2 mutations were found in five of 12 (42%) examined HCCs an d in three cases of adjacent non-neoplastic liver tissue (25%). There were three guanine to adenine (G --> A) point mutations in the tumour tissue. Al l three mutations found in non-neoplastic liver from VC-exposed patients we re also G --> A point mutations (codon 12- and codon 13-aspartate mutations ). Within the control group, K-ras-2 mutations were found in three of 20 (1 5%) examined HCCs. Conclusions: Mutations of the K-ras-2 gene in hepatocell ular carcinomas associated with VC exposure are frequent events. We observe d a K-ras-2 mutation pattern characteristic of chloroethylene oxide, one of the carcinogenic metabolites of VC analysed in animal models. Our results suggest that VC had direct toxic effects not only on endothelial cells but also on hepatocytes, as it was previously only described in animal models.