The epidemiological landscape of canine tumors in central Italy: animal cancer registry insights, distribution patterns, and incidence estimates.

BACKGROUND: Animal cancer registries (ACRs) monitor companion animal tumors, providing essential data for comparative oncology. Sharing domestic environments and possessing compressed lifespans, dogs serve as "One Health" environmental sentinels. OBJECTIVES: This study aimed to provide a descriptive analysis of canine neoplasms recorded in the ACR of the Lazio Region (central Italy) over 15-year period (2009-2023) and generate a survey-adjusted crude incidence estimate. METHODS: Primary tumors were standardized using Vet-ICD-O-canine-1. Proportional Morbidity Ratios (PMRs) were used to evaluate associations between demographic and environmental characteristics and the relative distribution of malignant tumor topographies. Incidence estimates were calculated using an adjusted canine population and corrected tumor counts to account for under-ascertainment. The population denominator was adjusted using a validated 75.3% registry completeness factor to calculate the annual crude incidence estimate. RESULTS: A total of 9,823 primary tumors from 9,122 dogs were included. Malignant tumors accounted for 59.3% of cases. Skin (38.4%), mammary gland (23.2%), and soft tissues (13.3%) were the most frequent topographies. The highest proportion of cases was observed in dogs aged 8-11 years. Among cases, 60.2% were purebred, 58.3% were fed industrial diets, and 49.1% lived primarily indoors. Females accounted for 57.7% of cases, although sex-stratified age-adjusted PMR analysis showed higher proportions of most tumors in males, except for mammary tumors (adj PMR = 46.22; 95% CI: 29.75-71.81). Intact females showed higher PMRs for mammary and female genital organs tumors, whereas spayed females had higher PMRs for hematopoietic, skin, digestive, and nervous system tumors. Higher PMRs for skin tumors were observed in dogs fed industrial diets, while environmental factors showed associations with specific tumor sites, including a higher frequency of skin tumors in outdoor dogs and a higher proportional frequency of mammary tumors in indoor dogs. The estimated crude incidence was 662.1 cases per 100,000 dogs, including 249.4 malignant and 412.7 benign tumors per 100,000 dogs. CONCLUSIONS: The ACR represents a valuable tool for monitoring canine cancer and exploring potential determinants of tumor occurrence. The integration of registry and survey data provided adjusted incidence estimates and improved the assessment of tumor burden. The findings support the use of ACRs in epidemiological surveillance and One Health research.