The main goal of Cancer vaccine is to help and treat cancer or to help keep it away from coming back after treatments. A cancer vaccine either treats existing cancer or prevents the cancer from developing. Vaccines that are able to treat existing cancer are therapeutic cancer vaccines and the others are "autologous" vaccines which is being prepared from samples like blood taken from the patient. They are specific to that patient only. Few researchers claimed that cancerous cells arises routinely are destroyed by the immune system mostly but tumors form when the immune system fails to destroy them.