Promoter hypermethylation of the p16 gene and loss of its protein expression is correlated with tumor progression in extrahepatic bile duct carcinomas.

CONTEXT: The p16 gene is one of the tumor suppressor genes, and its inactivation results in abnormal regulation of the cell cycle in human neoplasms. Promoter hypermethylation, a mechanism of p16 gene inactivation, has been reported to play an important role in tumorigenesis and to be related to patient prognosis in several carcinomas.

OBJECTIVE

To determine the role of the p16 gene in extrahepatic bile duct (EBD) carcinomas.

DESIGN

We examined promoter hypermethylation of the p16 gene using a methylation-specific polymerase chain reaction and the expression of the p16 protein using an immunohistochemical staining method in 90 cases of EBD carcinomas. We then compared the data with various clinicopathologic parameters, including survival rate.

RESULTS

Promoter hypermethylation was observed in 69 (77%) of the 90 cases. Of 69 hypermethylated cases, 32 (46%) demonstrated loss of p16 expression. Promoter hypermethylation of the p16 gene was more commonly observed in tumors with vascular invasion (22 [92%] of 24 cases) than without vascular invasion (71%, P = .03). Furthermore, p16 promoter hypermethylation with loss of p16 expression was more frequently observed in cases with lymph node metastasis (P = .006) and higher tumor stage group (P = .04). However, there was no significant difference in survival rate according to the status of p16 promoter methylation and/or p16 expression.

CONCLUSION

Promoter hypermethylation is an important mechanism in the inactivation of the p16 gene in EBD carcinogenesis. Furthermore, the loss of p16 expression, with or without p16 gene promoter hypermethylation, is closely related to the tumor progression in EBD carcinomas.