Immunosuppression and Human Malignancy

The immune system can deal effectively with the majority of viruses and bacteria, less effectively with parasites, and very poorly with cancer. Why is this so? Why are McFarlane Burnet''s and Lewis Thomas'' predictions that the immune system is in­ volved in ridding the body of cancer cells, encapsulated in the catchy phrase "immunologic surveillance," so difficult to experi­ mentally establish? C...