Is INI1-retained small cell undifferentiated histology in hepatoblastoma unfavorable?

Small cell undifferentiated (SCU) is a rare epithelial component of hepatoblastoma (HB), generally regarded as a high-risk histology for an adverse outcome. Limited data show that SCU cells in some HBs with poor prognosis had INI1 loss. Of note, SCU cells are usually INI1-retained in more typical HBs. We evaluated the clinical and pathologic characteristics of 7 HBs with SCU. Five patients were Children's Oncology Group stage I and underwent complete resection and adjuvant chemotherapy. Two patients with Children's Oncology Group stage III had neoadjuvant chemotherapy and liver transplantation. Six patients were alive without evidence of disease with a median follow-up of 5.4 years (range, 4-14.1 years). One patient died of transplantation-related complications 2.6 years after initial diagnosis. Small cell undifferentiated cells in 7 patients with HB were all INI-retained. Our results suggest that INI1-retained SCU may be not prognostically unfavorable. Immunohistochemical staining of INI1 should be performed in HBs with SCU.