Molecular alterations in retinoblastoma beyond RB1

Retinoblastoma is the most common malignant ocular tumor in children. Although RB1 alterations are most frequently involved in the etiology of retinoblastoma, candidate driver events and somatic alterations leading to cell transformation, tumor onset and progression remain poorly understood. In this study, we identified novel genomic alterations in tumors with a panel of 160 genes. Sanger sequencing and Multiplex Ligation-dependent Probe Amplification (MLPA) were initially performed for identifying patients without apparent RB1 alterations in blood DNA. Subsequently, NGS analyses of 24 paired (blood/tumor) samples of these patients were carried out for identifying somatic mutations and copy number variation in RB1 and other 159 genes. One novel pathogenic RB1 mutation and seven novel VUS were identified as well as 90 novel pathogenic mutations in 61 other genes. Twenty-three genes appeared exclusively mutated in tumors without altered RB1 alleles and three frequently affected biological pathways while five other tumors did not show pathogenic RB1 alterations or SNV/indels in 159 other genes. Curiously, deletion of GATA2, AKT1, ARID1A, DNMT3A, MAP2K2, MEN1, MTOR, PTCH1 and SUFU (in homo- or heterozygosity) were exclusively found in these tumors when compared to those with any pathogenic alterations, probably indicating genes that might be essential for the development of retinoblastoma regardless of a functional RB1. Identification of genes associated with retinoblastoma will contribute to understanding presently unknown aspects of this malignancy, which might be essential for its initiation and progression, as well as providing valuable molecular markers.