Epidemiology of skin tumor entities according to the new WHO classification in dogs and cats
A new or second edition of the international histological classification of skin, melanocytic and soft tissue tumors of domestic animals was published in 1998 with new entities and some new nomenclatures. For the period since then, we have not found a statistical study that discusses all these tumors in relation to the new WHO classification. ... Therefore, it has been the aim of this study to apply the new WHO classification in the epidemiology of the skin tumor entity. A statistical analysis of canine and feline skin tumors and tumor-like lesions was carried out using the diagnostic material of the Institute for Veterinary Pathology, Justus-Liebig-Universitaet Giessen, Germany. These comprised 816 skin tumors and tumor-like lesions in 768 dogs, and 197 skin tumors and tumor-like lesions in 194 cats. These lesions were classified according to the recommended WHO nomenclature and classification of tumors in domestic animals. Evaluation of the distribution of breed, age, sex, location and the tumor types was done in comparison with the prevalence of the same tumor in the literature. More than 25 % of the dogs in our collection were Mongrels, and the five most common breeds that were found in our collection were German shepherd dog, Boxer, Golden retriever, Westhighland white terrier and Cocker spaniel. The number of breeds in cats was less than in dogs, and the most common breed was Mongrel cats. The mean age of the skin tumor carriers in our collection was 7.5 years in dogs and 10.6 years in cats. The dominant skin tumor origin was epithelial with 49.3 %, while tumors of mesenchymal origin were 45.3 % and of melanocytic origin 5.3 % of all skin tumors and tumor-like lesion in dogs. In cats, the mesnchymal tumors were always the dominant group with 54.0%, followed by the epithelial tumors with 40.5 % and the melanocytic tumors with 1.5 % of all skin tumors and tumor-like lesions. The general sex distribution in dogs was 56.4 % male and 43.6 % female, while it was 55.5 % males and 44.5 % females in cats. The most common locations of the skin tumors and tumor-like lesions were limbs and head in both, dogs and cats. In our collection, 62 tumor types were found in the dog. The 10 most common skin tumors and tumor-like lesions in dogs were canine cutaneous histiocytoma, mast cell tumor, lipoma, hepatoid gland adenoma, infundibular cyst, fibrosarcoma, sebaceous hyperplasia, malignant melanoma, trichoepithelioma and melanocytomas, consecutively. 31 tumor types were found in the cat. The 10 most common skin tumors and tumor-like lesions in cats were fibrosarcoma, squamous cell carcinoma, apocrine adenoma, basal cell tumor, lipoma, trichoblastoma, ceruminous gland carcinoma, hemangiosarcoma, apocrine carcinoma and feline mast cell tumor, in this order. In our study, we have described for the first time the clear cell and cystic variants of trichoblastoma and reported the immunohistological expression of the canine granular cell trichoblastoma, which so far had been reported neither in the literature nor in the WHO classifications.We have discussed some other tumors and tumor-like lesions that are found in the literature and have not been classified in the new WHO classification.