Childhood Cancer Data Initiative Annual Symposium (Abstract Registration): Submission #69

Abstract Submission for Poster Presentation
-------------------------------------------
Abstract Title:: Expanding In Vivo Genotyping Across the Clinical Spectrum of Retinoblastoma: Aqueous Humor Liquid Biopsy Enables Comprehensive Biallelic RB1 Characterization Without Tumor Tissue
Abstract::
We previously established aqueous humor (AH) as a tumor-proximal liquid biopsy provides access to tumor-derived molecular information in retinoblastoma, a cancer in which diagnostic tumor biopsy is contraindicated. The critical next question was whether this signal could reconstruct the genotype of the living tumor—and whether molecular detectability persists when tumors are small and eye-sparing.

We analyzed diagnostic AH from 65 eyes of 53 patients using LBSeq4Kids, a clinically validated assay optimized for AH specimens. RB1 sequence variants, deletions, promoter alterations, and loss of heterozygosity were assessed, with germline RB1 status determined by blood testing when available. At least one RB1 alteration was identified in 57 of 65 eyes (87.7%), while complete biallelic molecular characterization was achieved in 53 eyes (81.5%). Importantly, molecular detectability was preserved across disease stage: complete characterization was 81.8% in B/C eyes and 81.1% in D/E eyes. At the individual alteration level, B/C eyes achieved 90.0% detection, comparable to published tumor-tissue cohorts (83.1–94.8%). AH captured the clinically relevant spectrum of RB1 alterations, including sequence variants, promoter alterations, deletions, and loss of heterozygosity. 

These findings advance AH liquid biopsy from detecting tumor-derived molecular signal to reconstructing the genotype of the living tumor. The preserved detectability in small, eye-sparing tumors indicates that AH can provide molecular access even when tumor tissue is unavailable. Because B–E disease represents the vast majority of eyes in large international clinical cohorts, this approach has the potential to expand molecular genotyping beyond tissue-accessible patients and enable multicenter studies linking RB1 genotype with clinical phenotype. 

Authors::
1. First Name: Liya
   Last Name: Xu
   Degree(s): PhD
   Organization: Children's Hospital of Los Angeles
2. First Name: Scarlet
   Last Name: Affa
   Degree(s): BS
   Organization: Children's Hospital of Los Angeles
3. First Name: Nerea
   Last Name: Goni
   Degree(s): Master
   Organization: University of Southern California
4. First Name: Laura
   Last Name: Kagami
   Degree(s): MD
   Organization: Children's Hospital of Los Angeles
5. First Name: Jaclyn
   Last Name: Biegel
   Degree(s): PhD
   Organization: Children's Hospital of Los Angeles
6. First Name: Jesse
   Last Name: Berry
   Degree(s): MD
   Organization: Children's Hospital of Los Angeles

Presenting Author:: Liya Xu
Institution:: Children's Hospital Los Angeles
Email Address:: liyaxu@usc.edu