PREVALENCE AND ETIOLOGY OF THE MOST COMMON MALIGNANT TUMOURS IN DOGS AND CATS

Summary Todorova, I., 2006. Prevalence and etiology of the most common malignant tumours in dogs and cats. Bulg. J. Vet. Med. , 9, No 2, 85 98. Cancer is a multistage process with a polyfactorial etiology. Its development results from the effect of various carcinogens such as ionized radiation, chemicals and oncogenic viruses. The impact of many endogenous factors  genetic, immune and hormonal, is also very important. Under the effect of these factors, changes in the DNA of genes often occur. Some dogs probably inherit some of abnormal genes that are precondition for the malignant cell transformation. The risk factors influence either directly or indirectly on tumour suppressor genes and oncogenes. Some DNA (herpes viruses, papova- and adenoviruses) and RNA viruses (retroviruses) are named tumour viruses as they are proved to cause cancer in infected cells. Unlike viral infections that are related only to some of neoplastic diseases, chemical carcinogens play a role in the development of most forms fo cancer. Food contains natural chemicals that could also lead to DNA damage and pro- duce cell alterations. The oncogenic effect of ionized radiation, depending on the dose, type of radia- tion and the way it was released is beyond any doubt too. Hormones are another endogenous factor important for the development of some cancer types, including mammary gland tumours. The present review summarizes the available literature data about the etiology and risk factors for development of malignant tumours in dogs and cats.