Feline Uveal Melanoma Review: Our Current Understanding and Recent Research Advances.

David Kayes,Benjamin Blacklock

doi:10.3390/vetsci9020046

Abstract

Melanocytic neoplasia is the most common form of ocular tumour in cats, accounting for 67% of cases in an analysis of 2614 cases of primary ocular neoplasia. Feline diffuse iris melanoma (FDIM) is by far the most common form of ocular melanocytic neoplasia, with limbal melanomas and atypical melanoma (melanoma affecting the choroid or ciliary body) infrequently recognised. Early lesions begin as flat areas of pigmentation of the iris, known as iris melanosis. This melanosis is a precursor lesion that can become FDIM when pigmented cells infiltrate the anterior iris stroma, commonly alongside a transition in cell morphology. The differentiation between FDIM and benign iris melanosis is only recognisable though histologic examination, with no in vivo means of identifying the malignant transformation. The behaviour of FDIM is variable and difficult to predict. Some FDIM lesions have a more benign progression and can slowly grow or remain static for years without affecting the ocular or systemic health of the individual, whilst other tumours behave aggressively, invading the ocular structures and significantly affecting the life expectancy of cats through metastatic disease. This makes management and timely enucleation of these cases challenging in practice. This article aims to review our current knowledge of FDIM.

Highlights

The average age of cats affected with feline diffuse iris melanoma (FDIM) is 9.4 years [1]with a reported range from 2 to 23.1 years [2,3,4,5,6]
Tumour progression was associated with a higher tumour fraction (TFx) and tumour-derived somatic copy number alterations (SCNA) (p ≤ 0.04) [35]
Iris biopsy should be considered to help confirm a diagnosis of early FDIM but must be interpreted with caution if a result of iris melanosis is obtained

Summary

Introduction

The average age of cats affected with feline diffuse iris melanoma (FDIM) is 9.4 years [1]with a reported range from 2 to 23.1 years [2,3,4,5,6]. Dysplastic features of the melanocytes were defined by Featherstone et al (2019) as plump, pigmented melanocytes with varying degrees of anisokaryosis with or without hyperchromasia and/or discernible nucleoli [5]. These precursor lesions are considered benign and are known as iris melanosis, where the melanocytes are confined to the anterior iris in 1–3 layers, regardless of the degree of melanocyte atypia. The behaviour of these lesions is unpredictable. The transition of iris melanosis to early FDIM is only recognisable histologically, where invasion of the dysplastic melanocytes into the iris stroma occurs [7]

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Discussion

Conclusion