The significance of autoimmune diseases increases day by day. Cancer is an important cause of mortality for which no definitive treatment has yet been found. Cancer can occur for many reasons. Studies have shown that autoimmunity underlies some types of cancer. On the contrary, antitumor immune responses may become cross-reactive with their own tissues, resulting in the development of autoimmunity. Further investigation of the relationship between autoimmunity and cancer will open new horizons for diagnosis and treatment of both groups of disease. This book presents studies of potential mechanisms linking autoimmunity and cancer and the relationship of malignancies with autoimmune disorders.