Every Tumour Counts: A Comprehensive Overview of Canine Oncology in Portugal.

Robust nationwide data on canine oncology in Portugal are scarce. We retrospectively reviewed 17,773 biopsy submissions received by a nationwide veterinary laboratory (2020-2024). After applying inclusion criteria, 6359 histopathology-confirmed tumours were analysed by behaviour, anatomical site, and host/geographical factors. Malignant and benign neoplasms occurred in near-equal proportions (50.4% vs. 49.6%). Tumour distribution was dominated by cutaneous/soft tissues (58.8%) and the mammary gland (24.1%), with all other sites individually rare. Dogs with malignant tumours were older than those with benign lesions (p < 0.001), and age differed by tumour behaviour and sex in two-way ANOVA (both p ≤ 0.001). Females accounted for 58.7% of submissions, and malignant disease was more frequent in females than in males (p < 0.001). Mixed-breed dogs formed the largest group; breed-specific logistic regression identified higher odds of malignancy in some pure breeds (e.g., Pug and American Staffordshire Terrier) and lower odds in others (e.g., Estrela Mountain Dog and Beagle). Multiplicity was recorded in a subset and was more common in females and in older dogs. Geographical analyses (NUTS2/NUTS3) showed, at most, weak regional variation and were not retained in multivariable models. These findings highlight the importance of early biopsy in new mass lesions, systematic mammary screening in bitches, breed-aware vigilance, and continued national surveillance to inform preventive care.