When a tumour appears to be locally advanced (i.e. invading a neighbouring structure or threatening to breach the circumferential resection margin), the use of neoadjuvant (preoperative) radiotherapy or chemoradiotherapy is usually considered. Long-course chemoradiotherapy is given as 5 fractions of radiotherapy combined with chemotherapy over a 6-week period. The aim is to down-stage the cancer and increase the chances of a complete resection with clear onco- logical margins. Alternatively, preoperative ‘short-course’ (5 days) radiotherapy can be used if the resection margins are not threatened but the cancer is still at high risk for local recurrence (e.g. peri-rectal lymph node involvement).