Chemo-immunotherapy of colorectal carcinoma: preclinical rationale and clinical experience

Advanced colorectal cancer is a common disease with an high mortality rate. For four decades, pharmacological treatment of the advanced disease was based on the use of 5-fluorouracil alone or in combination with biomodulators such as folinic acid and intereferon alpha. In the last 5 years, response to therapy has been considerably ameliorated thanks to the discovery of new drugs such as oxaliplatin and CPT-11. These agents, in combination with 5-fluorouracil, according to various schedules of treatment, have reached a significant improvement of palliation, response rate and survival. Immunotherapy is an uprising modality of treatment for human cancer including colorectal carcinoma. Its rationale is based on the knowledge that tumour cells are genetically unstable and produce molecular structures which allow their recognition and destruction by the immune-surveillance system. Therefore, humoral as well as cellular compartments of the immune system can be utilized according to a "passive" strategy (e.g. monoclonal antibody administration and adoptive immunotherapy) or an "active" approach, by using different modalities of vaccine therapy. In this context, monoclonal antibodies (mAbs) and cancer vaccines are being tested for the treatment of advanced colorectal cancer. Due to their genetic instability and extraordinary adaptative potential, tumour cells may acquire resistance to the immune effectors and mAbs exactly as they do for cytotoxic drugs. To improve the results of both immunological and chemical modality of cancer treatment, an increasing number of authors is starting to combine chemo and immunotherapy in the attempt to circumvent the limitations of both strategies. This report tries to review the possible rationale of the chemo-immunotherapy combination, illustrating preliminary results of preclinical and clinical studies.