Aqueous humor can be used as surrogate for retinoblastoma diagnosis, study suggests
Cleveland, Ohio: Aqueous humor sampling can serve as a surrogate for solid tumor sampling in cases of retinoblastoma, suggests a recent study. The pathogenic retinoblastoma (RB1) variants resulting from aqueous humor in all 3 eyes were consistent with direct tumor DNA sampling.
The findings, published in the Journal of American Association for Pediatric Ophthalmology and Strabismus (JAAPOS), indicate that specific testing can be performed even in the absence of enucleation as the AH can be assessed during treatment.
The study was conducted by Arun D. Singh, Department of Ocular Oncology, Cole Eye Institute, Cleveland Clinic, Cleveland, Ohio, and colleagues with the objective to demonstrate the feasibility of identifying a germline RB1 pathogenic variant in retinoblastoma from an aqueous humor sample.
For this purpose, the researchers obtained peripheral blood, fresh tumor tissue, and AH from 3 eyes of 3 RB patients who underwent enucleation at a tertiary eye care institute in the pilot case series. Following the isolation of the cell-free DNA (cfDNA), they performed sequence analysis of the RB1 core promoter and of exons 1 through 27, including nearby flanking intronic regions using a custom targeted hybridization protocol, followed by high-throughput sequencing.
3 enucleated eyes with advanced RB (group E [n = 2], group D [n = 1]) were included in the study cohort.
The findings of the study were as follows:
- In case 1, deletion of the RB1 promoter to exon 23 (delP->23) on both alleles was identified from the tumor as well as AH samples and absent in the blood sample, indicative of the absence of a germline RB1 pathogenic variant.
- In case 2, two heterozygous RB1 nonsense variants, c.610G>T p.(Glu204Ter) and c.751C>T p.(Arg251Ter), were identified in tumor and AH samples (allele frequency of 49% and 45%, resp.) and were absent in the blood sample, indicative of the absence of a germline RB1 pathogenic variant.
- In case 3, a heterozygous c.2326-14T>A substitution on allele 1 and loss of heterozygosity on allele 2 were identified in the tumor and AH (allele frequency of 97%), with the same heterozygous mutation in the blood sample, indicating the presence of a germline RB1 pathogenic variant.
"These findings support the concept that Aqueous Humor sampling can be a surrogate for solid tumor sampling in cases of Retinoblastoma," the authors concluded.
Reference:
Raval V, Racher H, Wrenn J, Singh AD. Aqueous humor as a surrogate biomarker for retinoblastoma tumor tissue. J AAPOS. 2022 May 13:S1091-8531(22)00102-1. doi: 10.1016/j.jaapos.2022.03.005. Epub ahead of print. PMID: 35577019.
