Frequent p16INK4a inactivation is an early and frequent event of intraductal papillary neoplasm of the liver arising in hepatolithiasis

Intraductal papillary neoplasm of the liver (IPNL) is a precursor lesion of intrahepatic cholangiocarcinoma (ICC) arising in hepatolithiasis. In this study, 98 foci of IPNL identified in 39 surgically resected hepatolithiatic livers were investigated for expression of p16(INK4a), cyclin D1, p21(WAF1/CIPI), p53, mouse double-minute 2 (MDM2), and pRb. In addition, methylation-specific polymerase chain reaction (MSP) for p16(INK4a) promoter region was performed in these foci. Nonneoplastic bile ducts from 11 hepatolithiatic livers, 5 histologically normal livers, and 9 cases of nonpapiltary conventional ICC were used as controls. Decreased expression of P16(INK4A) was seen in IPNL group 1 with mild dysplasia and continued along the progression of IPNL to ICC. The expression of cyclin D1, p21(WAF1/CIP1), and pRb gradually increased along the progression of IPNL to ICC and became significantly high in IPNL of group 3 (carcinoma in situ). The expression of p53 and MDM2 was increased in IPNL group 3 and group 4 with evident invasive carcinoma. MSP revealed that 54.6% of 44 IPNL foci harbored p16(INK4a) promoter hypermethylation, and such foci were significantly correlated with decreased expression of p16(INK4a), protein. Ki-67 labeling index exhibited a stepwise increase from IPNL group 1 to group 4. We conclude that p16(INK4a) inactivation, due mainly to its promoter hypermethylation, is a frequent and early event of IPNL and may be responsible for genetic and epigenetic alterations of other cell cycle regulators in IPNL. (C) 2004 Elsevier Inc. All rights reserved.