Hepatocellular carcinoma as a complex polygenic disease. Interpretative analysis of recent developments on genetic predisposition

The different frequency of hepatocellular carcinoma (HCC) in humans at risk suggests a polygenic predisposition. However, detection of
genetic variants is difficult in genetically heterogeneous human population. Studies on mouse and rat models identified 7 hepatocarcinogenesis
susceptibility (Hcs) and 2 resistance (Hcr) loci in mice, and 7 Hcs and 9 Hcr loci in rats, controlling multiplicity and size of neoplastic liver
lesions. Six liver neoplastic nodule remodeling (Lnnr) loci control number and volume of re-differentiating lesions in rat. A Hcs locus, with high
phenotypic effects, and various epistatic gene–gene interactions were identified in rats, suggesting a genetic model of predisposition to
hepatocarcinogenesis with different subset of low-penetrance genes, at play in different subsets of population, and a major locus. This model is in
keeping with human HCC epidemiology. Several putative modifier genes in rodents, deregulated in HCC, are located in chromosomal segments
syntenic to sites of chromosomal aberrations in humans, suggesting possible location of predisposing loci. Resistance to HCC is associated with
lower genomic instability and downregulation of cell cycle key genes in preneoplastic and neoplastic lesions. p16INK4A upregulation occurs in
susceptible and resistant rat lesions. p16INK4A-induced growth restraint was circumvented by Hsp90/Cdc37 chaperons and E2f4 nuclear export by
Crm1 in susceptible, but not in resistant rats and human HCCs with better prognosis. Thus, protective mechanisms seem to be modulated by HCC
modifiers, and differences in their efficiency influence the susceptibility to hepatocarcinogenesis and probably the prognosis of human HCC.