Liver tumors represent approximately 1% of all childhood cancers. There are approximately 100 to 150 new cases of liver cancer diagnosed in children each year in the United States. Hepatoblastoma, the most common malignant tumor of the liver, accounts for two-thirds of all liver cancer in children. Hepatoblastoma typically occurs in the very young child, with a mean age of onset between 18 to 20 months and 95% of cases occurring before 5 years of age. The incidence of hepatoblastoma has approximately doubled over the past few decades. Hepatoblastoma is considered an embryonal tumor because, histologically, tumor cells resemble cells seen in the developing liver.
Hepatocellular carcinoma is the primary liver malignancy occurring in older children and adolescents. Other, less common liver tumors include undifferentiated embryonal sarcoma, rhabdoid tumor, angiosarcoma, rhabdomyosarcoma of the biliary tract, cholangiocarcinoma, and other germ cell tumors. One-third of all tumors of the liver in children turn out to be benign entities that include vascular tumors (hemangioendotheliomas), mesenchymal hamartomas, and adenomas.
EPIDEMIOLOGY AND PATHOGENESIS
For reasons not fully understood, there is a male predominance in both hepatoblastoma and hepatocellular carcinoma, with a male-to-female ratio of approximately 1.5:1 in both tumor types. A number of molecular pathways have been implicated in hepatoblastoma, including the canonical β-catenin pathway, MYC activation, and more recently oxidative stress. As with most pediatric cancers, the underlying reasons as to how most individual children develop hepatoblastoma are largely unknown; however, in 5% to 10% of hepatoblastomas, well-studied genetic syndromes are observed.
Beckwith-Wiedemann syndrome (BWS) is an overgrowth syndrome characterized by high birth weight, macroglossia, omphalocele, and visceromegaly. Children with BWS are at risk of developing a spectrum of embryonal tumors. A national registry of children with BWS reports that the risk of children with BWS developing hepatoblastoma is 2280-fold higher than the general population and that the risk for hepatoblastoma was significantly higher than any other type of cancer in these children. Screening children with BWS with periodic abdominal ultrasonography and serum alpha-fetoprotein (AFP) levels is recommended, as they may be associated with detection of tumors at an earlier stage.
Familial adenomatous polyposis (FAP), an autosomal dominant syndrome characterized primarily by polyp growth in the colon beginning in adolescence and a very high risk of colon cancer in young adults, is also associated with a high risk of hepatoblastoma. Mutation in the causative adenomatous polyposis coli (APC) gene can be readily detected in children with hepatoblastoma who have a family history of early-onset colon cancer. These children are clearly at risk for polyps and colon cancer and need follow-up with lifelong surveillance. It is less clear how great the risk of carrying such a cancer predisposition is in other children with hepatoblastoma without a clear history of FAP, but it has been suggested that children with hepatoblastoma be screened for APC mutations and that asymptomatic children from ...