Morphologic and Biologic Characteristics of the Canine Cutaneous Histiocytoma¹

Five hundred and twenty canine cutaneous histiocytomas (CCH) that developed in the dog population of Alameda and Contra Costa Counties, California, during 3 years were collected. Morphologic studies confirmed the noninvasive character of the tumors and the proliferative histiocytic nature of the cells. The average annual incidence rate during the 3-year period was 117 per 100,000 dogs. Although the CCH occurred over most of the body, a high proportion were found on the head. Boxers and dachshunds had a significantly higher risk than all other breeds, and purebred dogs in general had a higher risk than crossbred dogs. A followup study of 230 cases indicated that CCH rarely recur at the site of excision, at a new site, or at 2 sites simultaneously. Widespread metastases or death as a result of CCH were not observed. Efforts to transmit this tumor to dogs and hamsters were unsuccessful as were attempts to detect viruses, bacteria, or fungi as etiologic agents. The findings of this study help to cstablish the CCH as a distinct entity and make it possible to differentiate it from various mesodermal neoplasms on the basis of morphologic, biologic, and epizootiologic characteristics.