P53 protein expression in hepatoblastoma: an immunohistochemical investigation

Hepatic tumors in children

Although they account for only 1% to 4% of solid tumors in children, hepatic tumors and pseudotumors offer a diagnostic challenge to the clinician seeing only an occasional case. Metastatic lesions such as neuroblastoma, Wilms' tumor, and lymphoma are the most common neoplasm seen in the liver, but 10 distinct primary tumors and pseudotumors of the liver occur with some regularity, and a few others may be seen rarely, including leiomyosarcoma, rhabdoid tumor, and endodermal sinus tumor. Five of these neoplasms--hepatoblastoma, infantile hemangio-endothelioma, mesenchymal hamartoma, undifferentiated embryonal sarcoma, and embryonal rhabdomyosarcoma of the biliary tree--occur only in children and are the major focus of the article.

Primary malignant epithelial tumors of the liver in children: a study of DNA content and oncogene expression

Primary malignant epithelial tumors of the liver (PMETL) are rare in the pediatric age group, and very little is known about their biology as compared with adult tumors. The prognostic value of the DNA contents measured by image analysis and expression of oncogene c-erb2 and tumor suppressor gene p53 were studied in 30 cases of PMETL in children, including 24 with hepatoblastomas (HB) and 6 with hepatocellular carcinomas (HCC). p53 overexpression was detected in 12 out of 26 cases (46.0%), or in 3 of 5 HCC and 9 of 21 HB cases. A relatively high concordance of staining was observed with the two antibodies used (clone DO7, Dako and clone DO1, Santa Cruz Biotechnology). c-erb-B2 did not yield the characteristic membrane staining in any of the 27 cases in which reliable staining was obtained. However, 1 out of 4 patients with HCC and 1 of 23 with HB revealed strong granular cytoplasmic staining in several neoplastic cells. Interestingly, these were two of the three aneuploid multiploid cases. DNA histograms of 13 out of 29 cases (54.8%) were classified as DNA aneuploid (5/6 HCC and 8/23 HB): nine were hyperdiploid, one was hypodiploid (1HB), and three were multiploid (2HB and 1HCC). In the HB group, DNA aneuploidy was strongly associated with embryonal histological areas, suggesting that a disturbance in the process of cell differentiation is associated with marked genetic aberrations. Only the group of HB was submitted to univariate analysis of survival by the Kaplan-Meier method for age (< 24 months vs. > or = 24 months), sex, preoperative chemotherapy (yes vs. no), residual disease (metastasis, and/or unresectable tumor), p53 expression by immunohistochemistry (positive vs. negative), and DNA ploidy (diploid vs. aneuploid). Only residual disease at the time of diagnosis (P < 0.017) and preoperative chemotherapy (0.030) were found to be negatively correlated with biological behavior, estimated as overall survival. DNA aneuploidy tumors (P < 0.125) and male patients (P = 0.123) showed a trend toward a more aggressive clinical behavior, although the difference was not statistically significant. Combining DNA ploidy and residual disease, patients were categorized into three groups: group I, patients with no adverse prognostic factors, i.e., diploid tumors without residual disease; group II, patients with only one adverse prognostic factor, i.e., aneuploid tumor or residual disease; and group III, patients with both adverse factors, aneuploid tumors and residual disease at time of diagnosis. A log-rank test comparing the three survival curves showed a statistically significant difference between them (P < 0.003). Although the series of cases is small, the results of this study highlight the importance of including DNA ploidy in the protocols designed for HB in children by international cooperative groups.

p53 in malignant and benign liver lesions

p53 expression was studied by immunohistochemical methods in benign and malignant human epithelial liver lesions in 46 patients from Hungary. Positive immunostaining for p53 protein, indicating the overexpression or prolonged half-life of p53 protein, was detected in the nuclei of tumour cells of seven of the 16 hepatocellular carcinomas (HCC) (44%), including three HCC patients with hepatitis B virus infection. Immunostaining of p53 was seen in one of the seven hepatoblastomas, none of the 17 focal nodular hyperplasias, and none of the six hepatocellular adenomas. The detection of p53 in a relatively high percentage of the HCC cases in Hungary, a country in which aflatoxin contamination of the diet is rare, suggests that factors other than aflatoxin led to the accumulation or overexpression of p53 in these patients.

Absence of p53 gene mutation and infrequent overexpression of p53 protein in hepatoblastoma

Ten cases of hepatoblastoma were studied for overexpression of p53 protein by immunohistochemistry and for possible p53 gene mutation by single strand conformation polymorphism (SSCP) analysis and direct DNA sequencing of the polymerase chain reaction products. Only one case of the macrotrabecular type at stage IV showed overexpression of p53 protein. No DNA mobility shift was found in any of these cases studied by SSCP analysis. DNA sequencing performed on the case showing overexpression of p53 protein revealed no mutation within exons 5 to 8. The associated adrenal cortical carcinoma of the same case also showed overexpression of p53 protein, but no mutation of the p53 gene. These results indicate that mutation of the p53 gene is infrequent in hepatoblastoma. This observation supports the view that mutation of the p53 gene is not as important in the oncogenesis of childhood neoplasms as in adult cancers.

Flow cytometric evaluation of nuclear DNA content in hepatoblastoma: further evidence for the inhomogeneity of the different subtypes

The DNA ploidy pattern of nine hepatoblastomas and three normal liver specimens was investigated by flow cytometry. Areas of unlike differentiation in the same tumor were investigated separately. Normal liver tissue and the fetal subtype were always diploid. Aneuploidy was found in the embryonal subtype. The one case of small cell tumor was also diploid. When the fetal and embryonal areas of the same tumor were analyzed together, there was always an aneuploid peak in the histogram. There are obvious differences in DNA ploidy among the various hepatoblastoma subtypes. Differences in methods used, including the failure in some studies to evaluate areas of unlike differentiation in the same tumor separately, probably account to some extent for the conflicting results of previously reported studies. When flow cytometric analysis of the DNA content of a hepatoblastoma is performed, it is important to ensure that the various types of differentiation in the tumor are represented adequately in the material investigated, especially when conclusions about the prognosis are to be based on these findings.