INI1 negative hepatoblastoma, a vanishing entity representing malignant rhabdoid tumor

MRT of the liver are rare tumors that comprise less than 5% of malignant pediatric liver tumors. They are currently diagnosed on the basis of documenting both INI1 negative immunoreactivity and rhabdoid morphology. In the absence of molecular testing, MRT lacking classic rhabdoid morphology are currently classified as small cell undifferentiated hepatoblastoma (HB). Here we report a case of MRT initially classified as a INI1 negative small cell HB. Whole Exome Sequencing with Transcriptome subsequently showed homozygous deletion of SMARCB1 on chromosome 22q11.23 with evidence of loss of expression of the gene, establishing the diagnosis of MRT. As molecular testing of these tumors is performed on a more routine basis, this case illustrates that the INI negative small cell undifferentiated variant of HB actually represents MRT, a tumor unrelated to HB.