The goal is to identify tumor margin (lower pole) to optimize the resection margin, and to limit resection of healthy rectal tissue for optimal anal sphincter preservation. Moreover, determining the optimal date of surgery following neoadjuvant radiochemotherapy in rectal cancer is being discussed and no consensus has been reached. Therefore, to date, there is no formal evaluation of tumor response. This is partly due to the lack of information on tumor state and tumor evolution over time, between the end of radiochemotherapy and surgery. Histological follow up of tumor would provide supporting information to fill this gap. However, frequent tumor biopsies are not possible. Alternatively, probe-based confocal laser endomicroscopy (pCLE) could allow for a sequential analysis of tumor response. Response to treatment could be assessed and used to define optimal date of surgical resection, depending on patient responding status to treatment. Responding patients would undergo surgery at a later date than non-responders, in whom surgery could be performed earlier.