International histological classification of tumours of domestic animals

Abstract

In 1966, WHO convened a meeting of investigators on comparative oncology, at which the participants agreed to start work on developing an international histologic classification of tumors of domestic animals in parallel with the classification of human tumors, being developed by WHO. The main purpose of the project is to reveal similarities and differences between tumors in man and domestic animals and thus provide a sound basis for research in comparitive oncology generally; a secondary aim is to help to advance veterinary pathology. A widely accepted standard nomenclature of tumors, based on defined histologic criteria, is necessary to avoid misunderstandings in the exchange of information and for collaborative work, such as coordinated epidemiologic and therapeutic studies. At present, uniformity in these matters is notably lacking: sometimes one term is used for different tumors and controversely, the same tumor may have several names. To ensure that the WHO histologic classifications of tumors in man were followed as far as possible, the veterinary pathologists who undertook these tasks consulted pathologists who had worked on those classifications. The basis for classification, as with the human tumors, has been mainly histology, but histogenesis and biologic behavior have been taken into account in some instances. This issue contains classifications of tumors of 10 body sites: lungs, hematopoietic and lymphoid tissue, thyroid gland, urinary bladder, nervous system, testis, skin, soft (mesenchymal) tissues, breast (including dysplasias), and eye and adnexa. The species covered are the 6 common domestic mammals: horse, ox, sheep, pig, dog and cat. However, in several classifications there is not enough material to enable all 6 species to be included. For example, the classification of mammary tumors is confined to the dog and cat, since tumors of this organ are rare in other species. In comparing the biologic behavior of tumors of domestic animals with that of human tumors, it should be borne in mind that euthanasia is usually carried out when the prognosis is hopeless and the animal is suffering. This may be before metastases have developed. The classifications can do no more than reflect the present state of knowledge, and modifications are almost certain to be needed in the light of future developments. It cannot be expected that all pathologists will agree entirely with the classifications, but it is hoped that they will adopt them for the sake of facilitating communication between cancer workers with different backgrounds, and especially between medical and vetinary pathologists.