General paucity of genomic alteration and low tumor mutation burden in refractory and metastatic hepatoblastoma: comprehensive genomic profiling study

Hepatoblastoma (HBL) is a hepatic malignancy of infants and young children, which is often cured by combinations of surgery and chemotherapy. Management of refractory and metastatic HBL is challenging. Comprehensive genomic profiling was performed on 31 refractory and metastatic HBL using a hybrid-capture, adaptor ligation-based next-generation sequencing assay. Tumor mutation burden (TMB) was calculated from a minimum of 1.11 Mb of sequenced DNA and reported as mutations/Mb. The results were analyzed for all classes of genomic alterations (GA). Activating CTNNB1 mutation was the most frequent GA seen in 19 (61%) of cases. All 3 (100%) mixed epithelial and mesenchymal HBL harbored CTNNB1 mutation. The small cell undifferentiated subtype showed SMARCB1 loss in both cases. There was no significant further correlation of GA with histologic subtype. In addition to the potential targeting of CTNNB1, other rarely identified possible targetable GA included ERBB4 (6%) and FBXW7, SRC and BRCA2 (each at 3%). The mean TMB was 3.5 mut/Mb, the median was 1.7 mut/Mb. There were 2 HBL with ≥10 mut/Mb. No alterations in TP53 were identified, and alterations in the DNA repair pathways were rare. Refractory and metastatic HBL is characterized by a general paucity of GA and is dominated by frequent CTNNB1 mutation and overall low TMB. Although potentially targetable GA are seen on occasion in HBL and a small number of cases have high TMB with potential to respond to immune checkpoint inhibitors, advanced HBL will remain a treatment challenge.