Osteosarcoma (OS) is the most common primary malignant bone tumor of mesenchymal origin. It is particularly difficult to treat because it is often resistant to chemo and radiotherapy, the basis of which is the induction of oxidative stress. We have previously shown that normal mesenchymal cells and OS cells differ in response to oxidative stress. In addition, OS cells differ depending on whether they are more or less differentiated. We have shown that cellular protective mechanisms for protection against oxidative stress are less efficient in more differentiated OS cells. In addition, differentiated cells contain more unsaturated fatty acids (UFAs), making them more susceptible to oxidative stress. Therefore, in this project we want to quantify individual UFAs and clarify the role of individual UFAs in sensitivity to oxidative stress, and examine their role in OS proliferation, invasiveness and migration and the response of the immune system related to UFAs. We will examine the differences in the response of OS and osteoblasts. We will examine the effect of UFA on the expression of cell membrane molecules important for OS malignancy, such as PD-L1 and E-cadherin. We will examine the effect of UFA on neutrophil migration and neutrophil-OS cell interaction, as well as the role of UFA in evading the immune response. We hope that the results of our research will help in understanding these processes and ultimately contribute to the further development of OS therapy.