Prevalence of cancer-should we screen?

JAVMA 2024

January 16, 2025

Jenna H. Burton, David M. Vail, Jennifer L. Willcox et al.

Background
Cancer screening in humans aims to detect malignancies at earlier stages to improve outcomes. In veterinary medicine, where cancer is the leading cause of death in older dogs, early detection of cancer may offer similar benefits. However, the prevalence of occult cancer in asymptomatic dogs is not well understood, limiting the predictive value of screening tests. This study sought to determine the prevalence of undiagnosed malignant neoplasms in healthy middle-aged to older dogs.

Methods
Healthy, client-owned dogs aged 5.5 to 11.5 years from breeds with higher cancer risk were screened between May 2019 and June 2022 for the Vaccination Against Canine Cancer Study (VACCS). Screening included:

-Physical examination with aspiration cytology of dermal/subcutaneous masses.
-Complete blood count, biochemical profile, urinalysis.
-Three-view thoracic radiographs and abdominal ultrasound.

Dogs with definitive cancer diagnoses or suspected malignancies were excluded from the study. Statistical analyses compared demographics and diagnostic findings.

Results
-Screened Population: 902 dogs, with a definitive cancer diagnosis in 24 (2.7%) and suspected malignancy in 30 (3.3%). Including suspected cases, the overall prevalence of cancer was 6.0%.

-Diagnostic Modalities:

-Physical examinations identified 83% of definitive cancers, primarily mast cell tumors, anal sac adenocarcinomas, and soft tissue sarcomas.
-Abdominal ultrasound and thoracic radiographs detected less frequent cancers and other lesions suspicious for malignancy.
-Routine bloodwork abnormalities contributed to two cancer diagnoses.

-Dogs with confirmed or suspected cancer were significantly older (median 8.0 years) than cancer-free dogs (median 7.0 years).

Limitations
-Cancer types such as bone or CNS tumors were likely underdiagnosed due to screening limitations.
-Findings may not generalize to all dog populations due to breed restrictions and inclusion criteria favoring healthier dogs.
-Cytologic evaluation by oncologists rather than pathologists for some cases could have affected diagnostic accuracy.

Conclusions
The prevalence of occult cancer in asymptomatic, high-risk middle-aged to older dogs is relatively low. Physical examination, including aspiration cytology of masses, remains the most effective screening tool for early detection of cancer in this population. Findings emphasize the importance of routine examinations and follow-up diagnostics for aging dogs at risk of cancer.

Prevalence of cancer in the population of dogs described in Table 1 compared between the overall population of dogs screened for the Vaccination Against Canine Cancer Study as compared to breeds at higher risk for cancer development that included Golden Retrievers (n = 134), Boxers (7), Bernese Mountain Dogs (17), and mixed-breed dogs (394). As some dogs were not definitively diagnosed with cancer but had lesions for which neoplasia remained a differential diagnosis, 3 separate analyses were performed to evaluate dogs that had been definitively diagnosed with cancer, dogs with a definitive diagnosis and that had lesions that were highly suspicious for cancer, and dogs that were definitely diagnosed and had any degree of suspicion that cancer was present.

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