Low prevalence of occult cancer diagnosis when screening healthy, higher-risk, middle-aged to older dogs.

Objective: To determine the prevalence of undiagnosed malignant neoplasms in a cohort of healthy middle-aged to older dogs.

Methods: Healthy, client-owned dogs between the ages of 5.5 and 11.5 years and of mixed breed or breeds overrepresented for death due to cancer were screened for eligibility to participate in the Vaccination Against Canine Cancer Study at 3 study sites from May 6, 2019, to June 21, 2022. Physical examination with rectal evaluation and aspiration cytology of dermal and subcutaneous masses, CBC, biochemical profile, urinalysis, 3-view thoracic radiographs, and abdominal ultrasound were performed to identify occult cancer or other serious disease in all patients prior to study enrollment.

Results: 902 dogs were screened for participation in the Vaccination Against Canine Cancer Study. At the time of screening, 24 dogs (2.7%) were diagnosed with cancer, while another 30 dogs (3.3%) had abnormalities identified for which malignant neoplasia could not be ruled out but was not definitively confirmed. The prevalence of confirmed cancer in this population was 2.7% and 6.0% when cases in which malignant neoplasia was suspected were included. For the 24 dogs definitively diagnosed with cancer, the diagnosis was made on the basis of physical examination with aspiration cytology of a dermal or subcutaneous mass for 20 dogs (83%).

Conclusions: Routine physical examination was able to detect the majority of the malignant tumors in this population of dogs.

Clinical relevance: A thorough physical examination, including rectal examination, with aspiration cytology of dermal or subcutaneous lesions is a critical component of cancer screening for middle-aged and older dogs.