The body has natural defenses against cancer even before the modern age, as evidenced by a plethora of research and meta-analyses show bing tumors can appear out of the blue, sometimes on their own, sometimes in response to a fever or disease. These days, immunosuppression is associated with a higher risk of cancer, and spontaneous tumor regression of untreated malignant tumors is recognized as an uncommon but real phenomenon. The standard treatment for bladder cancer since its successful demonstration in 1976 has been the intravenous infusion of live, attenuated Bacillus Calmette-Guérin bacteria. Tumor, host, and environment complex interactions are necessary for effective immunization against cancer. Since more people are paying attention to cancer treatment, cancer immunotherapy, which employs a variety of tactics to boost tumor immunity, marks a paradigm shift in the field.