Neoadjuvant Treatment Strategies for Locally Advanced Rectal Cancer

Abstract

Improved surgical technique plus selective preoperative radiotherapy have decreased rectal cancer pelvic local recurrence from, historically, 25% down to about 5-10%. However, this improvement has not reduced distant metastatic relapse, which is the main cause of death and a key issue in rectal cancer management. The current standard is local pelvic treatment (surgery ± preoperative radiotherapy) followed by adjuvant chemotherapy, depending on resection histology. For circumferential resection margin (CRM)-threatened cancer on baseline magnetic resonance imaging, downstaging long-course preoperative chemoradiation (LCPCRT) is generally used. However, for non-CRM-threatened disease, varying approaches are currently adopted in the UK, including straight to surgery, short-course preoperative radiotherapy and LCPCRT. Clinical trials are investigating intensification of concurrent chemoradiation. There is also increasing interest in investigating preoperative neoadjuvant chemotherapy (NAC) as a way of exposing micro-metastatic disease to full-dose systemic chemotherapy as early as possible and potentially reducing metastatic relapse. Phase II trials suggest that this strategy is feasible, with promising histological response and low rates of tumour progression during NAC. Phase III trials are needed to determine the benefit of NAC when added to standard therapy and also to determine if it can be used instead of neoadjuvant radiotherapy-based schedules. Although several measures of neoadjuvant treatment response assessment based on imaging or pathology are promising predictive biomarkers for long-term survival, none has been validated in prospective phase III studies. The phase III setting will enable this, also providing translational opportunities to examine molecular predictors of response and survival.

Keywords: Adjuvant chemotherapy; chemoradiation; neoadjuvant chemotherapy; preoperative radiotherapy; rectal cancer; surgery.