Pediatric liver tumors and hepatic ontogenesis: common and distinctive pathways

Teratoid Hepatoblastoma-Our Experience

Hepatoblastomas (HB) are the most common pediatric liver tumor with several subgroups described, of which teratoid HB is the rarest. The aim of this study is to characterize the histologic and phenotypic spectrum of teratoid HB in order to better understand the biology and behavior of these tumors. A retrospective analysis of all teratoid HB diagnosed at a major pediatric hospital as well as the consultation files of one of the authors (SR) was performed with the available clinical data and surgical pathology material reviewed. A detailed immunohistochemical workup was also performed. A total of 28 cases were included from patients ranging from 5 to 84 months of age and a M:F ratio of 1.07:1. Four patients had syndromic associations. In 14/28 cases, the tumors contained primitive glandular elements with histologic and immunophenotypic overlap with the yolk sac tumor which in two cases became predominant in metastatic sites. One case had extensive primitive neural epithelium mimicking a primitive neuroectodermal tumor (PNET). Other unique elements included melanin, mature neuroglial tissue, rhabdomyoblastic differentiation, and neuroendocrine carcinoma-like areas (n = 2). In conclusion, this study provides the largest series of teratoid HB to date with clinical and outcome data, highlights previously undescribed or under-recognized histologic patterns in these tumors, and describes the immunohistochemical profile of these tumors to aid in diagnosis.

‘Teratoid’ Hepatoblastoma: An Intriguing Variant of Mixed Epithelial-Mesenchymal Hepatoblastoma

Liver neoplasms are quite rare in childhood. They often involve 6.7 cases per 10 million children aged 18 years or younger. Hepatoblastoma (HB) is the most frequent tumor, but this neoplasm’s rarity points essentially to the difficulty of performing biologic studies and large-scale therapeutic trials. On the pathological ground, HB is separated into an entirely epithelial neoplasm or a mixed neoplasm with epithelial and mesenchymal components. This last category has been further subdivided into harboring teratoid features or not. The ‘teratoid’ HB includes a mixture of components with heterologous origin. The heterologous components include neuroectoderm, endoderm, or melanin-holding cells with or without mesenchymal components. The most important criterium for the teratoid component is neuroepithelium, melanin, and, more recently, a yolk-sac-like component and neuroendocrine components. The mesenchymal components include muscle, osteoid, and cartilage, which are most often observed mainly in ‘teratoid’ neoplasms. The teratoid component or mesenchymal components are diagnosed with biopsies. They appear more prominent after chemotherapy due to the response and shrinkage of epithelial elements and non- or low-responsive components of mixed HB. This review focuses on the clinical, radiological, and pathological findings of HB with teratoid features.

Current concepts in pediatric liver tumors

Liver tumors in children can be classified into benign or malignant; some of the benign lesions can have the potential of malignant transformation, and therefore the therapeutic approach may change. These neoplasms account for nearly 1-2% of all pediatric tumors and they have gained significant attention in the last decades due to data suggesting that the incidence may be increasing 5% annually. We know that with new and improved imaging modalities some of these lesions may be detected more often than before. Recent studies showed that liver cancer represented 2% of malignancies in infants by 1980s and this was doubled in incidence to 4% in the following 10 yr. In this review our aim is to discuss all primary liver tumors in children with attention to their clinicopathological and immunohistochemical features followed by the current standard of care.

HGF/c-Met related activation of β-catenin in hepatoblastoma

Background

Activation of beta-catenin is a hallmark of hepatoblastoma (HB) and appears to play a crucial role in its pathogenesis. While aberrant accumulation of the beta-catenin is a common event in HB, mutations or deletions in CTNNB1 (beta-catenin gene) do not always account for the high frequency of protein expression. In this study we have investigated alternative activation of beta-catenin by HGF/c-Met signaling in a large cohort of 98 HB patients enrolled in the SIOPEL-3 clinical trial.

Methods

We performed immunohistochemistry, using antibodies to total beta-catenin and tyrosine654-phosphorylated beta-catenin, which is a good surrogate marker of HGF/c-Met activation. CTNNB1 mutation analysis was also carried out on all samples. We also investigated beta-catenin pathway activation in two liver cancer cell lines, HuH-6 and HuH-7.

Results

Aberrant beta-catenin expression was seen in the cytoplasm and/or nucleus of 87% of tumour samples. Our results also revealed a large subset of HB, 83%, with cytoplasmic expression of tyrosine654-phosphorylated beta-catenin and 30% showing additional nuclear accumulation. Sequence analysis revealed mutations in 15% of our cohort. Statistical analysis showed an association between nuclear expression of c-Met-activated beta-catenin and wild type CTNNB1 (P-value = 0.015). Analysis of total beta-catenin and Y654-beta-catenin in response to HGF activation in the cell lines, mirrors that observed in our HB tumour cohort.

Results

We identified a significant subset of hepatoblastoma patients for whom targeting of the c-Met pathway may be a treatment option and also demonstrate distinct mechanisms of beta-catenin activation in HB.

Liver neoplasia in children

Management of pediatric liver tumors has significantly improved over the last 2 decades. The management options for hepatocelluar carcinoma (HCC) are not well defined. In the pediatric context, the main clinical aims are to reduce chemotherapy toxicity (predominantly ototoxicity and nephrotoxicity) in children treated for hepatoblastoma and to investigate additional modes of treatment for HCC. An increasing number of children develop HCC in the background of chronic liver disease, and screening methods need to be better observed.

Role of surgery in the management of soft tissue tumors

Pediatric soft tissue sarcomas (STSs), of which rhabdomyosarcoma is the most common, constitute approximately 5-6% of all cancers in children. Biopsy, being incisional or rarely excisional, is an essential primary diagnostic step, while in some cases it may be followed by primary re-excision to establish a correct diagnosis in which molecular analysis can be helpful. Most European STS treatment groups favor preoperative chemotherapy, sometimes combined with preoperative irradiation. Local therapy is essential, in which surgery remains an important adjunct. However, it has to be applied in a multidisciplinary, combined fashion in close cooperation with oncologists, pathologists and radiotherapeutists. Current 5-year survival in rhabdomyosarcoma reaches 60-70% in nonmetastatic cases and remains below 20% in metastatic situations. Outcome in pediatric nonrhabdomyosarcoma STS is similar.

[Hepatic tumors in childhood: experience on 245 tumors and review of literature]

This review on the pathology of hepatic tumors in childhood, from a personal series of 245 tumors, focuses on incidence, management, description of frequent tumors such as hepatoblastoma, fibrolamellar carcinoma, and undifferentiated sarcoma for malignant tumors, focal nodular hyperplasia, hepatocellular adenoma, and mesenchymal hamartoma for benign tumors. Malignant and benign entities of recent description, including the following: crowded, small cell undifferentiated and cholangioblastic variants of hepatoblastomas, mesenchymal hamartoma miming hepatoblastoma, liver adenoma and adenomatosis in diabete MODY3 families, gastrointestinal stromal tumor with liver metastasis associated to Carney triad, macronodules in non-cirrhotic portal fibrosis are reviewed. For each entity, the clinical presentation, the diagnostic criteria and the differential diagnosis are described. The role of immunohistochemistry and molecular biology in the diagnosis and identification of new molecular mechanisms triggered by oncogenic activation with new prognostic markers, and therapeutic targets is emphasized.