Prevalence and histopathological classification of equine melanocytic tumours in the Czech Republic and Slovakia.

Equine melanocytic tumours are of great concern for horse owners, especially those who own grey horses. These tumours can be initially benign but data from literature suggest that all equine melanocytic tumours have a potential to undergo a malignant transformation and even develop distant metastases. This study aimed to diagnose and classify equine melanocytic tumours, assess their prevalence in relation to the horse's coat colour, sex, and age, and evaluate their occurrence sites. Over the period of four years (2020--2023), biopsies and necropsies of 203 horses were performed; melanocytic tumours were diagnosed in 34 cases (16.75%). Based on the morphological features of the neoplastic cells and presence of distant metastases, 3 horses (8.82%) were diagnosed with early-stage melanocytic lesions, 10 (29.41%) with melanocytomas, 4 (11.76%) with low-grade melanoma, 8 (23.53%) with intermediate-grade melanoma, 6 (17.65%) with metastatic melanoma and 3 (8.82%) with high-grade anaplastic melanoma. There was a significantly higher prevalence of the most malignant types of melanocytic tumours (metastatic melanoma, high-grade anaplastic melanoma) in horses over the age of 15 years (70%, P < 0.05). [ABSTRACT FROM AUTHOR]