Any approach to the treatment and prevention of cancer must face the daunting reality that each cancer may be as individual as the patient in whom it has evolved. The challenge is also to develop a therapy that would eradicate that which is abnormal while preserving what is normal. For many years, therapies have been sought that could target a specific abnormal cancerous processes, such as rapid division or increased vascular flow, but with only limited success. Unfortunately, these successes have also been accompanied by varying degrees of toxicity and there is currently no standard therapy that can eradicate clinical disease and prevent recurrence while leaving normal tissue unharmed. However, approaches directed towards manipulating tumor-specific immunity hold promise for effective treatment and lasting cure. These approaches are based on the exceptional specificity of the immune system, the potential for long-term protective memory, and the accumulated evidence that affected individuals have spontaneous immune responses against their own tumors.