Tumor DNA sampling from aqueous humor in retinoblastoma – A report from South Asia

Purpose: Retinoblastoma (RB) is the most common intraocular tumor in pediatric age group. The role of genetics has been explored in predicting survival prognosis, but its role in predicting globe salvage remains largely unexplored. We hereby aim to isolate cell-free DNA (cfDNA) from aqueous humor (AH) in RB eyes and validate its use for genetic studies. Methods: AH was obtained from 26 eyes undergoing enucleation (arm A) or intravitreal chemotherapy (arm B). Isolation of cfDNA was done using QIAamp® Circulating Nucleic Acid kit, and the cfDNA was utilized for targeted sequencing of RB1 gene. Results: We could isolate cfDNA in all eyes (72% unilateral and 28% bilateral) with a distribution peak between 140 and 160 bp and a mean concentration of 27.75 ng/µl for arm A and 14 ng/µl for arm B. Targeted sequencing done on four samples showed RB1 gene mutations, namely, inframe deletion (c. 78-80del, p.Pro29del), start-loss mutation (c.1A>T, p.Met1?), nonsense mutations (c.2236G>T, p.Glu746Ter), (c.1659T>A, p.Cys553Ter), and (c.2065C>T, p.Gln689Ter), and novel missense mutations (c.672C>A, p.Asp224Glu) and c.692C>T (p.Pro231Leu). Genetic profile of cfDNA extracted from AH and genomic DNA from the tumor tissue was comparable. Conclusion: Our study supports the previous reports that AH may be used as a source of tumor-derived cfDNA. This is the first report from South Asia on isolation and genetic analysis of cfDNA from AH of RB eyes and, therefore, a big step forward in paving the role of tumor genetics in RB. Further studies are required to elucidate concordance between the tumor and AH genetic profile.