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

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.

Iridial melanocytoma in a ferruginous hawk (Buteo regalis): A case report and review of avian melanocytic neoplasia

“…Metastasis is most commonly reported in the liver, lung, kidney, and spleen 32 . It is important to note that even tumors with non‐metastatic behavior may warrant eventual enucleation due to secondary glaucoma from the mass effect blocking the irideocorneal angle 33 . In the case of the hawk discussed in this study, the behavior of this tumor is most similar to a benign melanocytoma as demonstrated by the low mitotic count and minimal cellular atypia of the mass.…”

“…32 It is important to note that even tumors with non-metastatic behavior may warrant eventual enucleation due to secondary glaucoma from the mass effect blocking the irideocorneal angle. 33 In the case of the hawk discussed in this study, the behavior of this tumor is most similar to a benign melanocytoma as demonstrated the low mitotic count and minimal cellular atypia of the mass. The hawk was followed for 3 years with no signs of adverse effects of the progression of the iridial mass except for ocular abnormalities, including cataract formation and a dyscoric pupil.…”

“…In humans and equids, cutaneous melanoma has been associated with increased sun exposure, but the influence of sun exposure on uveal melanoma is controversial 33,34 . The hawk in this case report lived in Fort Collins, Colorado and has likely had significant sun exposure at an altitude over 5000 feet.…”

“…In humans and equids, cutaneous melanoma has been associated with increased sun exposure, but the influence of sun exposure on uveal melanoma is controversial. 33,34 The hawk in this case report lived in Fort Collins, Colorado and has likely had significant sun exposure at an altitude over 5000 feet. In horses and humans, sun protection mechanisms, including sunglasses and ultraviolet filtering masks, have been used in clinical practice to prevent neoplastic processes, such as squamous cell carcinoma.…”

Advances in Understanding Spontaneously Occurring Melanoma in Animals

“…The most common is feline diffuse iris melanoma, which can have a poor prognosis if not removed early, due to the risk of systemic metastasis [ 11 ]. The review by Kayes and Blacklock examines the current knowledge of feline diffuse iris melanoma, ranging from diagnostic evaluation (including a full ocular examination, iris biopsy and histopathology), factors associated with metastatic disease (such as histological characteristics, circulating cell-free DNA, and infiltrating tumour lymphocytes), and gene expression and mutational analysis [ 12 ].…”