The characteristics of all somatic cells is their limited life duration and regulated proliferation, differentiation and survival necessary for the organism to function properly. The accumulation of cells that make up tissue without physiological function is called a tumor or neoplasm. One of the fundamental properties of a tumor is clonality, the emergence from a single cell that begins to proliferate. The uncontrolled growth characteristic of tumor cells arises as a result of impaired regulation of cellular systems. Cancer is the process of a series of changes in which certain cells gradually become malignant. Tumors that have the potential to spread to the organism in which they are produced are considered malignant. The causes of malignant transformations are related to external factors such as mutagens, that is, carcinogens, to errors in the mechanisms of the cell itself, such as a replication error, and viruses are one of the most important causes. Oncolytic viruses are viruses that multiply in tumor cells, kill them and spread among them without damaging or infecting non-tumor cells. Tumor viruses are not only important because they cause pain in humans, but also because they play a key role in cancer research by serving as models in molecular and cellular cell transformation studies, and thanks to advances in molecular cancer biology, improvements have been made in developing new approaches to cancer treatment . The objective of this thesis is to explain the properties of tumor cells, their formation and growth, to explain the impact of the virus on tumor formation, approaches to tumor treatment, and the importance of vaccination for the prevention of disease.