Chromosome 6p amplification detected in blood cell-free DNA in advanced intraocular retinoblastoma

ABSTRACT

Background

In patients with retinoblastoma, gains of chromosome 6p have been associated with less differentiated tumors. In cell-free DNA from the aqueous humor (AH), 6p gain has been associated with an increased risk of enucleation. While the identification of somatic copy number alterations (SCNAs) via the AH has been well established, these alterations are not routinely identified in the blood due to low tumor fraction.

Materials and methods

SCNAs were considered positive at 20% deflection from the baseline. Somatic RB1 pathogenic variants were identified with targeted sequencing using a panel including all RB1 exons.

Results

A 24-month-old patient presented with unilateral retinoblastoma (Group D/AJCC Stage cT2B) and was treated with primary enucleation. In the peripheral blood, a heterozygous mutation (c.3920T>A) in the APC gene was reported. Genomic analysis of the tumor and AH revealed two novel somatic RB1 mutations (c.1589_1590del and c.2330dupC). Both also demonstrated highly recurrent RB-related SCNAs. Chromosome 6p gain was detected in the blood with an amplitude suggesting approximately 12% tumor fraction. At a follow-up of 24 months, there has been no evidence of metastatic disease.

Conclusions

To our knowledge, this is the first time an SCNA has been detected in the blood of an RB patient, suggesting in some advanced eyes there may be a high enough tumor fraction to detect these alterations (>5% needed). It remains unclear whether 6p gain or increased tumor fraction in the blood is indicative of increased risk of metastatic disease or new primary cancer; studies to address this are ongoing.

KEYWORDS:

• Retinoblastoma
• aqueous humor
• blood
• liquid biopsy
• somatic copy number alterations

Disclosure statement

Drs. Berry, Xu, and Hicks have filed a patent application entitled, Aqueous Humor Cell-Free DNA for Diagnostic and Prognostic Evaluation of Ophthalmic. The following authors report no conflicts of interest: SS, MW, PK, RP, RS.

Additional information

Funding

This work was supported by Childhood Eye Cancer Trust, Wright Foundation, National Cancer Institute of the National Institute of Health Award K08CA232344, National Institute of Health P30EY029220, National Cancer Institute P30CA014089, Hyundai Hope on Wheels RGA012351, Knights Templar Eye Foundation, Institute for Families, Inc., Children’s Hospital Los Angeles, Larry and Celia Moh Foundation, Nautica Foundation, Research to Prevent Blindness, an unrestricted departmental grant, USC Dornsife College of Letters, Arts and Sciences, and the Berle and Lucy Adams Chair in Cancer Research. The A. Linn Murphree, MD, Chair in Ocular Oncology.