engleski

Comparative Veterinary Tumor Pathology

All animals develop neoplasms, either common to any species or specie-specific. Describing all animal neoplasms in detail is beyond the scope of our presentation. Therefore this presentation will emphasize frequent neoplasms of production animals, especially horses, cattle, small ruminants, cameloids, and lagomorphs. Other species developing neoplasms relevant to that species, or that serve as models for the study of human neoplasia will also be briefly discussed. Frequent tumors of production animals include equine sarcoid, benign and malignant melanomas, lymphomas, papillomas, equine granulosa cell tumor, squamous cell carcinomas, equine pituitary adenoma of pars intermedia, rabbit uterine adenocarcinoma, equine pedunculated mesenteric lipomas and Marek disease of chickens. Sarcoids are the most frequent equine neoplasms. Lymphomas are proliferations of neoplastic lymphoid cells of T, B, or non-T non-B phenotype able to affect any species at any age, and mimic several other pathological conditions. Several frequently occurring neoplasms have a viral etiology. Many are caused by different retroviruses: bovine and feline lymphomas, avian leukosis, enzootic nasal carcinoma and pulmonary adenomatosis of sheep, feline osteochondromatosis, murine mammary adenocarcinomas, and walleye (Stizostedion spp.) sarcoma. Others are associated to different viruses: equine sarcoid (bovine papillomavirus), papillomas (papillomaviruses), woodchuck (Marmota monax), heron and duck hepatocellular carcinomas (various hepadnavirus), Marek disease of chickens (herpesvirus), fibropapilloma of green see turtles (herpesvirus?), and renal adenocarcinoma of frogs (herpesvirus). Occurrence of some tumors is associated to parasitic infestations: esophageal and gastric sarcomas associated to spiruroid Spirocerca lupi in Canidae, cholangiocarcinoma in Felidae hosting liver flukes within bile ducts, gastric polyps in non-human primates with Nochtia spp., hepatic sarcomas in rodents associated to tapeworm larval stages. In animals, as in humans, genetic predisposition influences development of neoplasms. Some breeds are predisposed to develop certain neoplasms. For instance, gastric adenocarcinomas are observed in Belgian shepherd dogs but are rather rare in other canine breeds. Boxer dogs and other brachiocephalic canine breeds may develop many multiple tumors (e.g. mast cell tumors, gliomas, oral basisquamous cells carcinomas, hematopoietic, vascular, mammary, testicular neoplasms and others). Large canine breeds are more prone to develop osteosarcoma of long bones. Other tumors are hereditary, such as renal adenocarcinomas of German shepherds or melanomas in gray horses. Several exogenous agents are well-known carcinogens in humans and laboratory animals. In animals, neoplasms can also be induced or associated with foreign substances. Examples include osteosarcomas with metal implant in dogs, post-vaccinal sarcomas of cats, asbestos related mesotheliomas in several species, or cyclophosphamide-associated urinary bladder neoplasms in dogs. These exogenous agents may be part of the natural environment of animals. For instance, bracken fern is a well-recognized cause of urinary bladder neoplasm in cattle. Several spontaneous or experimental animal neoplasms are good models for the study of human neoplasia, such as the woodchuck WHV7 virus associated hepatocellular carcinoma. In addition, recent progress in gene transfer technology has permitted the development of large numbers of transgenic and knockout mouse models, which are extremely valuable for the study of cancer and which have tremendously contributed to our present understanding of neoplasia pathogenesis. The incidence of some neoplasms may vary depending on geographic location. This may be related to differences in culture or way of doing things. For instance, mammary, ovarian and testicular tumors are more frequent in countries were gonadectomy of domestic carnivores are not routinely performed. Canine transmissible venereal tumor is more common in parts of the world where dogs are not restricted to confined areas. Or this may be related to differences in exposure to specific carcinogens. Hence, cutaneous squamous cell carcinomas in white cattle and cats will mostly arise in parts of the world with heavy sun exposure. Veterinary pathologists are specialists with appropriate knowledge and training to properly interpret, diagnose and study pathological conditions in animals, including neoplasms. This gives them a unique opportunity to significantly contribute to the identification of new carcinogens or new mechanisms of cancer development. References are available upon request.

tumor pathology; animals

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