The cytogenetics of hepatoblastoma demonstrate recurring events which include whole chromosome trisomies, most commonly trisomy of chromosome 2, 8, or 10. In addition, unbalanced translocations involving a breakpoint on the proximal short arm of chromosome 1 are observed which result in a duplication of the long arm of chromosome 1q. The most commonly involved reciprocal chromosomal arm is 4q, although the reciprocal chromosome is highly variable and always results in a loss of chromosomal material. The full significance of these chromosomal changes has yet to be confirmed in large studies, however a suggestion of an association of duplication of regions of 2q with a poor prognosis. A rare sub-type of hepatoblastoma, known as the small cell undifferentiated variant, is associated with deletion or translocation of 22q, the locus of the rhabdoid tumor gene, SMARCB1.