Background Uveal melanoma is an aggressive ocular malignancy. Early molecular characterisation of primary tumours is crucial to identify those at risk of metastatic dissemination. Although tumour biopsies are being taken, liquid biopsies of ocular fluids may form a less invasive but relatively unexplored alternative. In this study, we aim to evaluate the DNA content of vitreous fluid from eyes with a uveal melanoma to obtain molecular information from the tumour.

Methods DNA was isolated from 65 vitreous fluid samples from enucleated eyes with a uveal melanoma and studied using digital PCR. Primary and additional driver mutations (in GNAQ, GNA11, PLCB4, CYSLTR2, BAP1, SF3B1 and EIF1AX) were investigated using accustomed targeted and drop-off assays. The copy numbers of chromosome 3p and 8q were measured using multiplex and single-nucleotide polymorphism-based assays. Our findings were compared to the molecular profile of matched primary tumours and to the clinicopathological tumour characteristics.

Results Almost all (63/65) vitreous fluids had measurable levels of DNA, but melanoma-cell derived DNA (containing the primary driver mutation) was detected in 39/65 samples (median proportion 18%, range 0.2%-94%) and was associated with a larger tumour prominence, but not with any of the molecular tumour subtypes. Among the vitreous fluids with melanoma-cell derived DNA, not all samples harboured (analysable) other mutations or had sufficient statistical power to measure copy numbers. Still, additional mutations in BAP1, SF3B1 and EIF1AX were detected in 13/15 samples and chromosome 3p and 8q copy numbers matched the primary tumour in 19/21 and 18/20 samples, respectively. Collectively, a clinically-relevant molecular classification of the primary tumour could be inferred from 27/65 vitreous fluids.

Discussion This proof-of-concept study shows that substantial amounts of DNA could be detected in vitreous fluids from uveal melanoma patients, including melanoma-cell derived DNA in 60% of the samples. Prognostically-relevant genetic alterations of the primary tumour could be identified in 42% of the patients. A follow-up study is needed to evaluate our approach in a prospective clinical context.

The authors have declared no competing interest.

This study was supported by the European Union's Horizon 2020 research and innovation program under grant agreement number 667787 (UM Cure 2020, R.J. Nell and N.V. Menger).

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The Biobank Committee and Medisch Ethische Toetsingscommissie of the Leiden University Medical Center gave ethical approval for this work (under numbers B14.003/SH/sh and B20.026/KB/kb).

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