This thesis aimed to investigate current knowledge of the pathophysiological mechanisms for the formation of mast cell tumours in different animal species and humans. Based on the available literature data, biological behaviour and forms of mast cell tumour occurring in animals and people have been compared. In addition, investigated have been essential features of mast cell tumours, such as incidence, the possibility of spread, and methods of diagnosis and treatment. The pathogenesis of mast cell tumour formation is not completely clarified. However, it is assumed that it is multifactorial, although a well-researched predisposition of breeds to mast cell tumour formation raises suspicion that pathogenesis is based on a genetic component. C-KIT mutations, marked with internal duplication, cause production of KIT receptor which is constitutively activated in the absence of a ligand, ie steam cell factor which leads to signal-regulated phosphorylation and play an essential role in the pathophysiological mechanism of the tumour. Mutations in c-KIT gene in dogs are associated with progression and poor prognosis of mast cell tumour. In contrast, such mutations are not associated with disease prognosis in cats and humans. However, they play an essential role in diagnosis and therapy in humans. The clinical manifestation and biological behaviour of mast cell tumours vary widely depending on the type of animal–ranging from benign individual masses to aggressive systemic tumours. However, in dogs, mast cell tumours are the most common malignant neoplasms on the skin. Unlike low-grade mast cell tumours, high-grade mast cell tumours often have a very poor prognosis and shorter survival time. In combination with conventional chemotherapy, the use of tyrosine kinase inhibitors (TKIs) in veterinary medicine has opened up a whole new perspective on the therapy of patients who do not respond to existing drugs. Current research focuses on developing a improving new treatment strategies. In addition, comparative pathology and oncology can contribute to the development of research, diagnosis, more accurate prognosis and therapy of human and animal mast cell tumours.