Antiepidermal growth factor receptor radiosensitizers in rectal cancer

The activation of the epidermal growth factor receptor (EGFR) pathway correlates with a worse prognosis in many solid tumours. Hence, EGFR inhibitors have been developed as a treatment for cancer. The EGFR inhibitor cetuximab has been successfully combined with radical radiotherapy in head and neck cancer. In metastatic colorectal cancer, cetuximab and panitumumab have activity as single agents, and increased response rates are achieved when added to standard chemotherapy schedules. This approach of using EGFR inhibitors has also been extrapolated to the preoperative treatment of locally advanced rectal cancer. Counterintuitively, the combination of chemotherapy, EGFR inhibitors and anti-VEGF antibodies seem to show lower response rates, suggesting antagonism. In rectal cancer, disappointingly low pathological complete response (pCR) rates have often been observed in chemoradiation regimens using EGFR inhibitors. In this study, we aimed to examine the rationale for the integration of EGFR inhibitors into chemoradiation schedules for rectal cancer. We have reviewed the clinical evidence and potential mechanisms for an interaction when EGFR inhibitors are added to fluoropyrimidine-based preoperative chemoradiation, the majority of which have used cetuximab. The primary outcome measure used was pCR. The overall pooled pCR for cetuximab-based chemoradiation was 10.71% (38/356). The rate of G3/G4 gastrointestinal toxicity, in terms of diarrhoea, varied from 5 to 30%, with an overall pooled rate of 13.8% (49/353). A better understanding of the mechanisms involved in combining chemotherapy and radiotherapy might allow more effective future scheduling of biological and chemical agents in combination with radiation.