Aqueous Humor: A Liquid Biopsy for Retinoblastoma

Measurable amounts of tumor DNA - genetic information from the tumor found in the aqueous humor of the eye.

Retinoblastoma treatment may be ready for a revolution. Retinoblastoma is a tumor of that starts in the retina that generally affects children under the age of 5. Retinoblastoma may result in loss of one or both eyes, if not diagnosed early. Because it occurs in the inner part of the eye, retinoblastoma cannot be biopsied unlike most cancers that are diagnosed using a biopsy. This is because oncologists can only access the tumor if the affected eye is removed (called enucleation) in the course of treatment. This fact has made it difficult to use available information to optimize treatment. Recent study gives proof of concept for a safe and effective way to derive genetic information from the tumor without removing the eye. The study was conducted by a team at the Vision Center of Children’s Hospital Los Angeles and the University of Southern California (USC) Roski Eye Institute, part of Keck Medicine of USC, provides. The findings are published in JAMA Ophthalmology.

Retinoblastoma was one of the first tumors to have its genetic origin identified; the RB1 retinoblastoma tumor suppressor gene mutation was discovered by A. Linn Murphree, MD, a co-author on this paper, who established the Retinoblastoma Program at Children’s Hospital Los Angeles. However, ocular oncologists have been limited in their ability to use this genetic information to inform diagnosis and the application of personalized treatments since removing tissue from the tumor in the back of the eye could spread tumor cells outside of the eye or even to the rest of the body, resulting in a far worse prognosis for the patient.

Retinoblastoma - Causes, Symptoms, Diagnosis, Treatment & Prevention
Retinoblastoma is a type of cancer of the eye occurring in children. Early diagnosis and treatment, and genetic counselling can go a long way in saving life and vision in children and siblings at risk for this disease.

‘Chromosomal changes from DNA found in the aqueous humor corroborates the chromosomal changes found in the retinoblastoma tumor.’

Retinoblastoma treatment

Retinoblastoma is treated using chemotherapy given either intravenously or through the ophthalmic artery. There are limits, however, to the amount of drug that actually reaches the eye. As a result, relapse does occur due to small tumor particles that break off - or seed - from the main tumor. The treatment for these seeds changed dramatically in 2012 when intraocular injections of chemotherapy were shown to be safe and effective. In order to inject chemotherapy directly into the eye, it is first necessary to remove a small amount of fluid, called aqueous humor, from the front of the eye, to decrease the pressure within the eye prior to injection of the medication.

Why throw the fluid?

Oncogene 'MDM4' Plays a Critical Role in Cancer Cell Growth in Retinoblastoma
The MDM2 oncogene plays a critical role in promoting expression of the MYCN oncogene that is required for growth and survival of retinoblastoma cells.

Previously, this fluid was simply dispensed after the procedure. "Just as I was discarding the aqueous humor, I wondered if there was a possibility it contained tumor-derived genetic material we could use to better treat our patients," said Jesse Berry, MD, ocular oncologist at CHLA, assistant professor of Clinical Ophthalmology at the USC Roski Eye Institute and first author on the study. "In fact, we found measurable amounts of tumor DNA - genetic information from the tumor that had previously been completely unavailable from an intact eye."

"Chromosomal changes from DNA found in the aqueous humor corroborates the chromosomal changes found in the retinoblastoma tumor," said James Hicks, PhD, professor of Biologic Sciences at the USC Michelson Center for Convergent Bioscience and professor at the Keck School of Medicine at USC. "These findings provide proof of principle that the aqueous humor can be used for a surrogate ’liquid’ tumor biopsy."

Triple-Drug Chemotherapy With Topotecan Helps Prevent Secondary Leukemia In Retinoblastoma
Topotecan can be used in front-line therapy of retinoblastoma and reduce exposure to drug etoposide, which is associated with secondary leukemia.

Overview of the study

The study reported on six samples from three eyes affected with retinoblastoma, in children less than 3 years of age. Two of the eyes had been removed primarily for treatment of the disease; the third eye was receiving intraocular injections as therapy but ultimately had to be removed due to disease recurrence. Aqueous humor was taken from all three eyes and allowed investigators to compare tumor DNA in the aqueous humor to DNA found in the retinoblastoma tumor.

Smartphone Cameras are the New Age Diagnostic Tool for Detecting Retinoblastoma
When a tumor grows inside a child's eye, it can reflect back as a white pupil in flash photos. If spotted early, it could save a child's vision and life.

Revolutionizing retinoblastoma treatment

"Until now, we could only do genetic analysis - and base therapy on the specific pathologic tumor features - when there was no longer a possibility of saving the eye," said Thomas C. Lee, MD, director of the Vision Center at CHLA and associate professor at the USC Roski Eye Institute. "In the future we hope to have the capability to specifically target therapy to the type of tumor and can anticipate better outcomes for children with retinoblastoma."

The team of investigators plans future studies to compare tumor DNA from eyes that have been saved to those that need to be removed due to tumor recurrence.

"This research has the potential to completely transform how we treat children with retinoblastoma," said Jonathan W. Kim, MD, director of the Retinoblastoma Program at CHLA and also director of the ocular oncology service at USC Roski Eye Institute. "This is one of the most significant findings in retinoblastoma research in the past 20 years."

Source-Eurekalert