Spontaneous retinoblastoma-like mass in the retina of a young cynomolgus macaque

Abstract

Purpose : To characterize the morphology and functional impact of a spontaneous retinoblastoma-like mass in the retina of a young cynomolgus macaque.

Methods : A 4-year old, treatment naïve, female cynomolgus macaque of Mauritius origin was noted to have an intraocular mass during a routine clinical ophthalmoscopic examination. Color fundus photography, fluorescein angiography (FA), and optical coherence tomography (OCT) were conducted approximately 3.5 months after initial tumor discovery. Scotopic and photopic full-field electroretinography (ffERG) and flash visually evoked potential (fVEP) testing was conducted approximately 5 months after discovery.

Results : On indirect ophthalmoscopy a large (3 by 5 optic disc diameters), chalky white, irregular mass in the region of the macula which spared the right optic disc was observed. The retina was grossly detached 1 to 2 disc diameters around the mass. No other ocular abnormalities were noted in this eye or the left eye. Assessed on fundus photography, the tumor was vascular, occupied an area approximately 3 by 5 disc diameters, and detached an area of the retina approximately 6 by 7 disc diameters. OCT showed a solid tumor that was both intraretinal and subretinal with surrounding subretinal fluid. Fluorescein angiography showed hypervascularity and late staining of the tumor. Amplitudes of scotopic and photopic A- and B-waves in the affected eye were reduced approximately 30% when compared to the contralateral eye with minimal change in latency. Amplitude of the fVEP was reduced and mildly delayed.

Conclusions : Based on the data available, this mass is likely a malignant retinoblastoma. The mass is a single, unilateral tumor, suggesting somatic rather than germ line mutation. Electrophysiologic testing is consistent with early stage retinoblastoma. We have not observed similar retinal tumors in the thousands of cynomolgus macaques examined over the past two decades. Thus, the finding is rare in our cohort of animals. These findings illustrate the importance of baseline ocular examinations in preclinical toxicity studies.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

Composite color image of fundus. The tumor is vascular, spares the optic disc, and detaches an area of the retina.

 

OCT shows a solid tumor that is both intraretinal and subretinal.