Host response to colorectal cancer.

It has long been established that inflammation and immunity play critical roles in the pathogenesis, control and eventual metastasis of cancers. With the advent of more sophisticated animal models and immunohistochemical techniques a greater understanding of the immune system and its interactions has occurred. Individual immune cells are dynamic structures that have variable behaviour controlled by complex interactions in the tumour microenvironment. In the setting of colorectal cancer it was first observed that peritumoral inflammatory infiltrates were associated with improved prognosis. Immunohistochemistry has shown the individual cells types within these infiltrates. It now appears that an adaptive immune response, differentiated along the T-helper 1 pathway controls tumour invasion and metastasis. Furthermore, the immune system exerts selection pressure leading to the evolution of tumour cell variants that can induce tolerance and disable adaptive immunity. These tumour cells then use the mechanisms of innate immunity to facilitate further growth, angiogenesis, invasion and eventual metastasis. These issues are investigated with particular relevance to colorectal cancer. Using the immune response to defeat CRC has been under intense investigation but has so far been unsuccessful. Nevertheless, researchers remain optimistic that immunotherapy will play an important role in the treatment of this common disease.