Cancer and autoimmune diseases are connected in several ways, as both involve abnormal immune system activity. In some cases, cancer can trigger the development of autoimmune conditions, while autoimmune diseases may increase the risk of certain cancers. For example, patients with rheumatoid arthritis or lupus may have a higher risk of developing lymphoma. Additionally, some cancer treatments, like immune checkpoint inhibitors, may inadvertently activate autoimmune responses. Research is focused on understanding how cancer alters immune function and how to harness the immune system more effectively to target tumors without causing autoimmune side effects. Advances in immunotherapy are offering new hope, as these therapies aim to reprogram the immune system to attack cancer cells while minimizing harm to healthy tissues.