Clinical, histopathological, and molecular characterization of canine pigmented viral plaques.

Canine pigmented viral plaques (PVPs) are proliferative epidermal lesions caused by canine papillomaviruses (CPVs). Although the lesions are benign, neoplastic transformation has been reported. Cases reported in the literature are few and mainly focused on genome sequencing. The aim of this study was to collect data on the epidemiology, clinicopathological features, and genotyping of PVPs. Fifty-five canine PVPs were retrospectively retrieved and histologically evaluated. Follow-up was available for 33 cases. The median age was 6.5 years and pugs were the most represented breed (25%). There were 4 clinical presentations: a single lesion (24%), multiple lesions (75%) in one (41%) or different sites (34%), and generalized lesions all over the body (24%). The abdomen and axillae were the most common sites. In single lesions, no recurrence was observed after conventional surgery, whereas different medical treatments reported for multiple lesions were not successful. Spontaneous regression was reported in 3 cases. Neoplasia in contiguity with PVPs was seen in 5 of 55 lesions (9%), and 1 dog was euthanized due to invasive squamous cell carcinoma (SCC). The most useful histopathological features for diagnosis were scalloped profile, epidermal spikes, hypergranulosis, and hyperpigmentation. L1 immunolabeling was present in 14 of 16 cases (87%). Sequencing revealed that 10 of 16 cases were associated with CPV-9 (71%), 2 cases were associated with CPV-4 (14%), and 2 cases were associated with CPV-8 (14%). In conclusion, this represents a large cohort study on canine PVPs reporting data on clinicopathological features, therapy, outcome, and the type of CPV involved for the first time in Italy.