Melanocytic ocular and periocular tumours of the horse

Extensive intraocular melanoma with secondary glaucoma in a 15-month-old Thoroughbred filly

A 15-month-old, grey, Thoroughbred filly presented for investigation of a 6-week history of corneal oedema and blepharospasm on the right eye (OD). The filly was otherwise healthy. Following ophthalmic examination, glaucoma on the OD was diagnosed. A space occupying mass within the anterior chamber was documented on transpalpebral ultrasonographic examination. This mass obliterated most of the anterior intraocular structures on the peripheral nasal side (corneal endothelium and drainage angle), leading to secondary glaucoma. After systemic and topical treatment addressing secondary glaucoma, the corneal oedema reduced. The mass was visualised as an irregularly rounded brown structure associated with the iris on the peripheral nasal side of the anterior chamber. Given the filly's signalment, location and appearance of the mass, a tentative diagnosis of intraocular melanoma was made and enucleation was performed. Histopathological evaluation of the globe revealed solid sheets of heavily pigmented melanocytic cells, disrupting the normal ciliary body architecture and extending into the iris and subretinal. The cells were pleomorphic, polyhedral to round with occasional spindle-shaped cells, and contained moderate to large amounts of granular black-brown pigment (melanin). The iridal component expanded into the anterior chamber, with cells directly opposed to Descemet's membrane, with loss of the endothelium and expanding and occluding the filtration angle in this area. The lesion infiltrated locally into the edge of the sclera, but did not extend through the sclera, though occasional perivascular clusters of melanophages were observed within the scleral stroma adjacent to the optic nerve. Diagnosis of a uveal melanocytic neoplasm was confirmed, with characteristics similar to only one reported case . This is a unique case of a rapidly growing, invasive, uveal melanoma in a young horse. Intraocular melanoma should be considered as a differential diagnoses for glaucoma in grey horses, regardless of the age and absence of melanocytic skin lesions.

Noninvasive diode laser-an effective and safe treatment of iris cysts in 46 eyes of 35 horses

BACKGROUND

Iris cysts in horses are often asymptomatic and noticed incidentally. However, cysts can cause local corneal oedema and erratic behaviour like shying, decreased performance and head-shaking.

OBJECTIVES

To describe the use of diode laser as a noninvasive treatment option for iris cysts in the horse and to document factors influencing its efficacy, associated complications, long-term outcome and rate of recurrence.

STUDY DESIGN

Retrospective case series.

METHODS

Case records of horses treated for iris cysts by diode laser at the Utrecht University Equine Clinic were reviewed between 2008 and 2020. Diagnosis was based on ophthalmic and ultrasonographic evaluation. Long-term follow-up was obtained in two phases, a telephone survey with the owner and a photographic re-evaluation of the treated eyes.

RESULTS

Thirty-five horses were included, with a total of 46 eyes treated. One day after diode laser treatment (short-term), 35/46 treated eyes had a good decrease in cyst size, 7/46 had a moderate effect, 1/46 had a minimal effect, 1/46 had no effect, and in two cases the effect was unspecified. The decrease in size after diode laser treatment in polycystic eyes (odds ratio [OR] 0.381, 95% CI 0.1530-0.724), p = 0.001), thick-walled cysts (OR = 0.139; CI = 0.023-0.726, p = 0.02) and hyperplastic corpora nigra (OR = 0.081; CI = 0.004-0.528, p = 0.03) was significantly less satisfactory, with ORs of 0.381, 0.139 and 0.081, respectively. Minor complications, such as mild reactive uveitis, were reported in 8/46 (17%) eyes. On long-term follow-up (median 19 months; IQR 25.5), clinical signs had diminished or disappeared in most cases (93%) and 83% of the owners would recommend the treatment. Based on long-term photographic re-evaluation (median 32.5 months; IQR 49.75), 2/16 cases of recurrence were seen.

MAIN LIMITATIONS

Retrospective design, follow-up by telephone questionnaire and photographic re-evaluation. Loss to follow-up in the photographic re-evaluation.

CONCLUSIONS

Both short- and long-term results indicate diode laser treatment is a useful and safe option for iris cyst size reduction, with a low risk of recurrence. Presurgical ultrasonography is recommended to assess the feasibility of treatment and to allow for better surgical planning.

Effects of Topically Applied Betulinic Acid and NVX-207 on Melanocytic Tumors in 18 Horses

Simple Summary

Melanomas are skin tumors of the pigment-producing melanocytes. Equine melanomas are among the most frequently diagnosed tumors affecting grey horses. The melanocytic tumors progress to malignancy in more than two-thirds of cases. Previous laboratory experiments and studies with horses utilizing the naturally occurring betulinic acid (BA) and its derivative NVX-207 showed promising results with respect to the topical (epicutaneous) treatment of equine melanoma. Therefore, the aim of this feasibility study was to gain first insights into the effect and safety of BA and NVX-207 in eighteen horses with early-stage melanocytic tumors after a 13-week-long topical application. The topical treatment was convenient and safe. Compared to a placebo, the data suggest a positive treatment effect from topical application of BA and NVX-207 on equine melanomas toward the end of the treatment period. However, the time period studied was too short to conclusively prove this. Further advancement of the investigational medicinal products studied herein could lead to an effective, topical and marketable novel drug which helps to relieve suffering and, consequently, improve the welfare of equine skin cancer patients.

Abstract

The naturally occurring betulinic acid (BA) and its derivative NVX-207 induce apoptosis in equine melanoma cells in vitro. After topical application, high concentrations of the substances can be reached in healthy equine skin. With the aim to investigate the effect and safety of topically applied BA and NVX-207 in horses with melanocytic tumors, the longitudinal, prospective, randomized, double-blind, placebo-controlled study protocol included eighteen Lipizzaner mares with early-stage cutaneous melanoma assigned to three groups. Melanocytic lesions were topically treated either with a placebo, 1% BA or 1% NVX-207 twice a day for 91 days. Caliper measurements, clinical examinations and blood tests were performed to assess the effects and safety of the medication. The topical treatment was convenient and safe. The volumes of tumors treated with BA were significantly reduced over time as compared to tumors treated with the placebo from day 80 of the study. Although treatment with NVX-207 seemed to decrease tumor volume, these results did not reach statistical significance. The findings must be regarded as preliminary due to the limited group size and need to be replicated in a larger cohort with modified pharmaceutical test formulations. Accordingly, the treatment protocol cannot yet be recommended in its current form.