Molecular and immunohistochemical study of the inactivation of the p16 gene in primary hepatocellular carcinoma.

OBJECTIVE: To determine whether p16 gene is involved in the genesis of primary hepatocellular carcinoma (HCC). METHODS: Twenty-five HCC tumor samples with corresponding non-tumor liver tissue specimens were examined for p16 gene alterations. The identification of deletion of exon 1 and exon 2 in p16 gene was performed using comparative multiplex polymerase chain reaction (PCR) analysis. The point mutation of exon 2 in p16 gene was investigated by single strand conformational polymorphism (SSCP) analysis, and the status of p16 gene methylation was screened using a PCR based methylation analysis. 35 parafin-embedded specimens of HCC with corresponding non-tumor liver tissues, including the 25 cases described above for screening p16 gene alterations, were investigated for p16 protein expression using immunohistochemical analysis. RESULTS: Among 25 cases, 2 homozygous deletions and 1 hemizygous deletion were found in HCC samples. No point mutation was identified in the remaining 22 tumor samples without p16 gene deletions. Hypermethylation was detected in 24% (6/25) of tumor samples. However, the corresponding non-tumor liver tissue specimens were always unmethylated at the p16 locus. Loss of p16 protein expression occurred in 16 of 35 (45.7%) tumor samples, and all the non-tumor liver tissue specimens showed positive p16 staining. For the 25 cases examined for p16 gene alterations, the loss of p16 protein expression was observed in all tumors with p16 gene alterations and also in 3 tumors without p16 gene alterations. CONCLUSION: Inactivation of the p16 gene may play an important role in the genesis of primary hepatocellular carcinoma.