Descriptive epidemiology of canine and feline cancer in California, United States from 2000 to 2019

Cancer is a leading cause of morbidity and mortality in middle- to old-aged dogs and cats, yet detailed epidemiological data remain limited. This study investigated the distribution of nine major cancer types in dogs and cats using hospital records from the Veterinary Medical Teaching Hospital at the University of California, Davis (2000-2019). Sarcoma, carcinoma, lymphoid neoplasia (LN), mast cell tumor (MCT), and melanoma were analyzed using multivariable logistic regression to assess associations with breed, age, and sex-neuter status. Among 150,063 patients (79.9% dogs; 20.1% cats), 26,883 were diagnosed with cancer (18.1% of dogs; 17.0% of cats). Older age was the strongest predictor of these cancers in both species, though odds of sarcoma, LN, and MCT declined in senior dogs (≥12 years). The following associations were specific to dogs. Spayed females had higher odds of LN (OR=1.43), MCT (OR=1.92), and melanoma (OR=1.63) compared to intact females, whereas neutering had no significant effect in males. Male dogs had higher odds of LN than females, both intact (OR=1.59) and spayed/neutered (OR=1.15), while spayed females had higher odds of MCT than neutered males (OR=1.28). Sarcoma and carcinoma odds varied by age and sex-neuter status, with significant interactions. Aging more strongly affected sarcoma in females regardless of neuter status and carcinoma in intact females and neutered males. Intact females consistently had lower odds of sarcoma but higher odds of carcinoma in old age. These findings highlight complex, cancer-type-specific associations. A California-wide cancer registry would provide a more comprehensive picture of cancer epidemiology in companion animals. • Large-scale analysis: Retrospective study of 150,063 dogs and cats at a tertiary veterinary • hospital over 20 years (2000–2019). • Cancer trends: Incidence declined over time in cats; remained stable in dogs. • Age as key risk factor: Risk increased with age in both species; some cancer types • declined in senior dogs (≥12 years). • Sex-neuter associations: Spayed female dogs had higher odds of lymphoid neoplasia, • mast cell tumor, and melanoma; neutering had no significant effect in males. • Interaction effects: Significant interactions between age and sex-neuter status affected • risk for sarcoma and carcinoma. • Call to action: Findings highlight the need for a dedicated companion animal cancer • registry