Evidence for the existence of cancer immunosurveillance

The original concept that immune systems could recognize and control cancer was first postulated by Ehrlich and later embodied in cancer immuno-surveillance hypothesis of Burnet and Thomas in the 1950's and 60's. Their hypothesis was largely abandoned a decade or so later because of the absence of solid evidence to support this idea. Fortunately, cancer immuno-surveillance has continued to be vigorously debated and experimentally tested, and now as we enter the 21^st century, mounting evidence in humans and mice supports the involvement of immunity in tumor initiation, growth and metastasis. The concept that the immune system detects stressed, transformed and frankly malignant cells underpins much of the excitement currently surrounding new immuno-therapeutic options in cancer treatment. Paradoxically, while strong evidence exists that immuno-surveillance systems operate at early stages of tumorigenesis, established tumors primarily induce immune tolerance. To avoid immunity, tumors must develop mechanisms that inhibit the generation and detection of pro-inflammatory danger signals. In this review, we will define the cancer immuno-surveillance hypothesis, summarize the historical circumstances that led to its conception and debate, and discuss more recent convincing experimental evidence that supports this and other emerging concepts about the cancer: immunity interface.