# Risk Factors for the Occurrence of Cutaneous Neoplasms in Dogs: A Retrospective Study by Cytology Reports, 2019–2021

## TL;DR

This study identifies risk factors for skin tumors in dogs in an arid region of Mexico, revealing unique patterns influenced by local environmental and demographic factors.

## Contribution

The study provides novel epidemiological data on canine cutaneous neoplasms in arid regions, highlighting distinct risk factors and malignancy patterns.

## Key findings

- A high malignancy rate of 56.59% was observed, with transmissible venereal tumor and mast cell tumors being the most common.
- Young dogs (0–4 years) had the highest malignancy rates, primarily due to endemic transmissible venereal tumor in intact animals.
- Schnauzers showed significantly lower odds of malignancy compared to mixed-breed dogs.

## Abstract

Cutaneous neoplasms represent a significant health concern in dogs worldwide, yet epidemiological data from arid regions remain limited. This retrospective study analyzed 698 canine cutaneous neoplasms diagnosed via fine needle aspiration cytology in Mexicali, Mexico, where extreme desert conditions create unique environmental challenges. We found a notably high malignancy rate (56.59%), exceeding reports from temperate regions. Transmissible venereal tumor (TVT) and mast cell tumors comprised 28.35% and 27.84% of malignant cases, respectively. A paradoxical age distribution emerged, where young dogs (0–4 years) showed the highest malignancy rates, driven by endemic TVT affecting intact animals. Conversely, Schnauzers demonstrated protective effects against malignancy compared to mixed breeds. These findings reveal how regional factors (intense UV radiation, limited reproductive control, and local canine population management practices) create distinct cancer patterns in arid environments. Understanding these unique patterns is crucial for developing targeted prevention strategies, improving diagnostic approaches, and optimizing treatment protocols in settings where cytology frequently guides clinical decision-making.

Studies worldwide report cutaneous neoplasms in dogs; however, data in the arid regions of Mexico remain scarce. Here we report the main malignant cutaneous neoplasms diagnosed by fine needle aspiration cytology (FNAC), and describe the associations with age, sex and breed in Mexicali. Neoplastic lesions accounted for 25.52% (698/2735) of the cases, of which 56.59% (395/698) were malignant. The highest prevalence was observed in dogs aged 9–12 years (n = 193), intact males (n = 162), and mixed-breed dogs (n = 247). Round cell neoplasms (n = 309), including lymphoma, transmissible venereal tumors (TVT), and mast cell tumors (MCT), were the most common cell lineage. Using dogs aged 0–4 years as the reference group, dogs aged 9–12 years had 0.241 times the odds of developing malignant neoplasms (95% CI: 0.141–0.415, p = 0.0025). Using neutered males as the reference group, intact females showed 2.499 times the odds of developing malignant neoplasms (95% CI: 1.462–4.271, p = 0.0042). Compared to mixed-breed dogs, Schnauzers (OR = 0.161) showed significantly lower odds of malignancy (95% CI: 0.082–0.317, p = 0.0004), while Pitbull Terriers had 1.748 times more chance of present malignant neoplasia (95% CI: 1.014–3.013, p < 0.0001). This study provides significant epidemiological evidence on canine cutaneous neoplasms in an arid region of Mexico, identifying key risk factors and distribution patterns that can guide preventive, diagnostic, and therapeutic strategies tailored to regional characteristics.