EN
The paper describes two cases of sarcoids in horses non-responsive to therapeutic procedures. Microscopic examinations of tumor tissue revealed the presence of an evident difference in the degree of collagen fiber synthesis between both examined tumors. The nuclear expression of proliferate antigen Ki 67 was significantly higher in the tumor tissue exhibiting low collagen fiber synthesis. The differences in the microscopic structure between these 2 tumors were reflected in the degree of differentiation between the cells of the tumors. The paper also discussed the ethiopathogenesis of equine sarcoids and the animals’ immune status role in the disease development and progress, as well as the latest methods used in effective sarcoid therapy.