Cell-Free DNA Tumor Fraction in the Aqueous Humor Is Associated With Therapeutic Response in Retinoblastoma Patients

Purpose: The aqueous humor (AH) liquid biopsy enables in vivo evaluation of tumor-derived cell-free DNA (cfDNA) from retinoblastoma (RB) eyes. Herein, we test our hypothesis that longitudinal dynamics of AH cfDNA-including tumor fraction (TFx) and somatic copy number alteration (SCNA) amplitude-correspond to therapeutic response. Methods: Eyes with >= 3 AH extractions during intravitreal chemotherapy (IVM) or at secondary enucleation between 2015 to 2019 were included. AH cfDNA was sequenced to assess RB SCNA amplitude; ichorCNA software was used to estimate TFx. Eyes without SCNAs or with TFx < 0.10 across all samples were excluded. Therapeutic responses for each eye were determined from clinical records. Statistical analyses included Mann-Whitney U and Pearson correlation tests. Results: Twenty eyes of 20 patients underwent >= 3 AH extractions; 6 eyes lacked SCNAs or had TFx < 0.10 throughout sampling and were excluded. Clinical progression was associated with significantly higher SCNA amplitudes and TFx values than regression (P <= 0.04). Relative increases in TFx (Delta TFx 1.86 +/- 2.22) were associated with disease progression, whereas relative decreases in TFx (Delta TFx 0.53 +/- 0.36) were associated with disease regression (P < 0.00001). A >= 15% increase in TFx relative to baseline during treatment was associated with an over 90-fold increased likelihood of clinical progression (odds ratio = 90.67, 95% confidence interval = 8.30-990.16, P = 0.0002). TFx and SCNA amplitude were significantly positively correlated throughout sampling (P <= 0.002). Conclusions: Longitudinal changes in AH-derived cfDNA TFx and SCNA amplitude are concordant with clinical responses of intraocular RB during active therapy. Translational Relevance: Longitudinal evaluation of AH cfDNA may provide an objective, quantitative way to monitor therapeutic response and disease burden in RB patients.