Object of the study - mammary gland tumours in the dog. Aim of the study - based on pathomorphological investigations, to study the frequency of diagnosis, morphological, pathogenetic, clinical, anam-nestic, and prognostic features of different histological types of mammary gland tumours in dogs of the city of Kyiv. Methods - pat-homorphological, histochemical, morphometric, clinical, biochemi-cal, statistical methods. Novelty - for the first time in Ukraine, ori-ginal studies have been conducted, to study mammary gland neo-plastic diseases in dogs living in conditions of a big town; own sug-gestions have been offered, regarding improvement of the principles of their classification; a number of indices have been determined, which promote development of mammary gland tumours of differenthistological types; the necessity has been grounded, of establish-ing a unique State centre for diagnosis and study of animal tumo-urs. Results - qualitative and quantitative spectra of histological types of mammary gland tumours in the dog have been identify-ed; morphological characterization of pleiomorphism of epitheli-al cells and their nuclei is given; data have been obtained on the features of DNA content in nuclei and intensity of cell death in different mammary gland tumours. A comparative analysis be- tween histological diagnoses, which were determined according to WHO classification of dog and human mammary gland tu-mours, has shown that an adequate classification of mammary gland tumours - along with standard histological characteristics - should take into account both sources of specific types of tumoral cells, that underlies the modern version of tumour classification in the dog, and localization of the primary lesion, as well as infil-trative properties of tumours that constitute the key principles of human mammary gland tumour classification. Differences have been established in time of appearance and speed of development of benign and malignant mammary gland tumours, their localiza-tion, size, and importance of atypical hyperplasia in the develop-ment of the latter, which allowed to identify a number of prog-nostic factors. It has been concluded that the risk of development of mammary gland tumours was increasing with each case of physiological and especially pathological estrogenic stimulation of mammary gland epithelium. Study results are being used in practice, educational process, and research work. Field of application - veterinary medicine.
