Small cell undifferentiated variant of hepatoblastoma: adverse clinical and molecular features similar to rhabdoid tumors.

Background: Small cell undifferentiated (SCU) histology in patients with stage I hepatoblastoma (HB) predicts an increased risk of relapse. We sought to determine the significance of SCU histology in patients with unresectable HB.

Procedure: Patients enrolled on the pediatric Intergroup (INT0098) trial for HB and patients from the personal consultation files of two of the authors (MF, LG) were reviewed for cases with SCU histology. These patients were compared with SCU HB patients identified by literature review.

Results: Eleven patients were studied. All patients with reported AFP results exhibited normal or minimally increased serum AFP levels. None of the patients survived: 10 died of disease progression, and 1 died from treatment complications. Immunostaining revealed that tumors from six of six patients tested were INI1 negative. Cytogenetic and molecular abnormalities in one patient (and two patients from the literature review) were similar to those described in rhabdoid tumors. Comparison with patients from the literature review revealed similar results except that 4 of 29 patients survived without evidence of disease.

Conclusions: SCU histology in HB patients is associated with an adverse outcome. These tumors appear to be biologically different from non-SCU HB. Evaluation of patient characteristics and outcomes for children with SCU HB and/or those with low AFP levels should be determined from large cooperative group studies. In the meantime, we suggest patients with unresectable HB containing SCU elements have careful cytogenetic, molecular, and immunohistochemical evaluation to ascertain rhabdoid features and receive treatment that differs from that provided for other HB patients.