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

## TL;DR

This study analyzed over 6,000 confirmed canine tumors in Portugal to identify patterns in tumor types, locations, and risk factors, offering insights for better prevention and care.

## Contribution

The study provides the first comprehensive nationwide analysis of canine tumor data in Portugal, revealing breed-specific and sex-related trends in tumor malignancy.

## Key findings

- Skin/soft tissue and mammary gland tumors were most common, with malignancy more frequent in older dogs and females.
- Certain purebred dogs like Pugs had higher odds of malignancy, while others like Beagles had lower odds.
- Tumor multiplicity was more common in females and older dogs, but geographic variation was minimal.

## Abstract

This five-year nationwide study analysed canine tumour biopsies submitted across Portugal. From 17,773 biopsy submissions, 6359 histopathology-confirmed neoplasms were included to describe tumour origin, frequency of malignancy and the types of dogs most affected. Almost four in five tumours were located in the skin/soft tissues (58.8%) or mammary gland (24.1%, predominantly in females), whereas neoplasms of the gastrointestinal tract, oral cavity, eyes, urinary system and other organs were comparatively uncommon. Dogs with malignant neoplasms were older than those with benign lesions. Mixed-breed dogs constituted the largest group; among purebreds, some breeds (e.g., Pug and American Staffordshire Terrier) had higher odds of malignancy, whereas others (e.g., Estrela Mountain Dog and Beagle) had lower odds. Multiplicity of tumours (subsequent tumours recorded over time) were more frequent in females and in older animals. Spatial analyses showed at most weak regional variation. For owners and clinicians, these findings support prompt assessment of any new mass, routine palpation of mammary chains in bitches and breed-aware vigilance, and they highlight the need for continued national surveillance to track trends and to guide prevention and care.

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.