Tumor heterogeneity in small hepatocellular carcinoma: Analysis of tumor cell proliferation, expression and mutation of p53 and beta-catenin

Most hepatocellular carcinomas (HCCs) first occur as well-differentiated HC Cs, from which poorly differentiated HCC cells develop because of dediffere ntiation. In this study, we try to clarify the changes of dedifferentiation and cell proliferative activity and their relationship in small HCCs (less than 3.0 cm in diameter) and try to learn the mechanism of these changer b y analysing the expressions and genetic changes of proliferation-related ge nes p53 and beta -catenin, or 41 surgically resected small HCCs, 11 were id entified to have tumor heterogeneity. DNA from the 11 small HCCs, consistin g of 29 intratumoral lesions and II noncancerous liver tissues adjacent to HCCs, was extracted from paraffin embedded tissue sections. Exons 5-8 of p5 3 gene and exon 3 of beta -catenin gene were amplified by polymerase chain reaction and analyzed by direct sequence. The serial sections were also imm unostained by anti-Ki-67, p53 and beta -catenin antibody. Immunohistochemis try showed that the p53 overexpression was significantly related to the pro liferative activities as evaluated by Ki-67 immunostaining and to the histo logical differentiation. The expression of beta -catenin was found to be he terogeneously distributed not only in various histological grades of the sa me tumor but also in areas of the same histological grade. p53 and beta -ca tenin gene mutations were detected in I tumor respectively, both of which w ere second primary HCCs and also recurred later. The p53 mutation showed th e same mutation pattern in heterogeneous subpopulations. beta -catenin muta tion was detected only in the less differentiated lesion but not in the wel l-differentiated lesion of tumor. In conclusion, our findings suggest that there was histological heterogeneity in small but established HCC, which wa s accompanied by increased proliferative activity and p53 overexpression. T he overexpression of beta -catenin may be related to the proliferative acti vity and dedifferentiation of HCC, (C) 2001 Wiley-Liss. Inc.