A Comparative Study of Melanocytic Tumours: Linking Portuguese Dogs and Cats to Human Cases.

Melanocytic tumours (MT) occur in both humans and companion animals, presenting an opportunity for comparative oncology research. Thus, this study provides a comprehensive epidemiological analysis comparing MT in Portuguese dogs, cats and humans. Data were obtained from the Portuguese National Cancer Registry (RON) (2011-2021) and Vet-OncoNet (2020-2023), utilising standardised oncological classification systems (ICD-O-3.2 and Vet-ICD-O-canine-1). The results indicate that Melanoma was the most frequently diagnosed MT across all three species, while melanocytomas were common in dogs but rare in cats and humans. A higher incidence rate (IR) for MT was observed in dogs (IR = 16.1) compared to humans (IR = 8.1) and cats (IR = 6.3), and neutered dogs (10.8 years) were diagnosed at significantly older ages than intact ones (9.9 years). Shar-Peis (RR = 14.2, p