Every organism has regulatory mechanisms that control cell proliferation, differentiation, and survival. Various factors such as chemical carcinogens, UV radiation, hormones, viruses and bacteria have a negative effect on the regulatory mechanisms, leading mainly to the development of malignant cells. In tumor cell cultures, continuous growth of cells can be observed as they are able to produce growth factors independently. Carcinogenesis is a complex process in which oncogenes and tumor suppressor genes play an important role. Oncogenes arise from protooncogenes through mutational activation, whereas tumor suppressors lead to the development of malignant tumors through their inactivation or loss of function. In tumors, unregulated control of the cell cycle is observed, with checkpoints that stop proliferation in the presence of damaged DNA. The aim of this thesis is to describe the types of tumors, explain their development and characteristics, various causes and genes associated with their development. Special emphasis is given to the different approaches for the treatment and prevention of tumors.