Epidemiology of Canine Cutaneous Histiocytoma: Insights From Age and Topographic Clustering

BACKGROUND: Canine cutaneous histiocytoma (CCH) is a benign Langerhans-cell tumour that often regresses spontaneously via inflammation. OBJECTIVES: To estimate incidence and characterise age and breed-anatomical-site patterns using two complementary clustering analyses. MATERIALS AND METHODS: A total of 359 histopathologically-confirmed CCHs from a private veterinary laboratory in Portugal (January 2020-January 2022) were analysed with dog-population denominators from the national registry (SIAC). Incidence rates (IR) were calculated for Lisbon-Setúbal; breed- and sex-specific relative risks (RR) were estimated. Age was modelled with BIC-selected Gaussian mixtures; breed-site patterns were summarised by hierarchical clustering of site frequencies (heatmaps). RESULTS: Cases concentrated in young dogs (≤ 2 years, 48.8%) and males (58.5%). Age clustering defined three bands (≈ ≤ 1.5, 1.5-3.5, > 3.5 years) with differing breed and site distributions. Breed-site clustering revealed recurring anatomical predilections by breed and sex. The annual IR in Lisbon-Setúbal was 4.0 per 10,000 dogs (3.5 in females; 4.4 in males). Risk was highest in French bulldogs (RR 11.5; IR 34.1) and Boxers (RR 8.3; IR 24.5) versus mixed-breed dogs (p < 0.001). CONCLUSIONS AND CLINICAL RELEVANCE: Canine cutaneous histiocytoma (CCH) shows clear age bands and breed-linked anatomical predilections; these patterns help prioritise ages, sites and breeds for studies of inflammation-mediated regression.