Primary cancers can be prevented by immunizations. We suggest immunizing healthy people, especially the ones with genetic predisposition to cancer, with a standard oncoantigen. In patients suffering from cancer, immunotherapy can be effective only if it is administered during complete remission. Immune competent cells, like T-lymphocytes and bone marrow, are the most important components for cancer prevention and treatment. Because of the dramatic increase in the incidence of cancer, it is important to offer all adults with absolutely healthy immune system an opportunity to donate their own T-lymphocytes and bone marrow cells and preserve them at -196^。C. These cells can later be used by the same people in auto-system if they develop cancer. Patients who had their cancerous tumors surgically removed can also have their own T-lymphocytes and bone marrow cells collected during remission and then used in auto-system in case of cancer reoccurrence. It is also possible to impact on cancer development during the process of cancerogenesis by administering large amounts of normal DNA and possibly different types of RNA (displacement) together with nucleases (directly into the tumor or blood). In addition, blockers of cytokines that suppress immune system should be administered as well. It is intriguing to think that injection of large amounts of normal DNA and possibly different types of RNA together with nucleases to patients with chronic and hereditary diseases (diabetes Type II, schizophrenia, and other similar diseases) can lead to therapeutic effect.