There is considerable evidence that the immune system is able to recognize tumors as being different from normal tissue. However, the strength of the signal to the immune system from most tumors, both in humans and laboratory animals, appears to be very weak. There is little evidence that the immune defense mechanisms are able to successfully inhibit neoplastic growth once a tumor has developed. The ability of a malignant cell to stimulate a host response must arise from differences between the molecular composition of the cell surface compared to that of its normal counterpart. Throughout this century many attempts have been made to stimulate the body's immune reaction to cancer cells to destroy metastases. However, little impact on treatment has been made. Part of the problem is the complexity of the immune system. The monoclonal antibody technology now offers hope that such complex systems may be broken down into their constituent parts and used to help treat patients with malignant diseae. In this way we may be able to analyze the very small differences between tumor and normal cells. There are now many reports of MCA's being raised against human solid and blood malignancies.
