The LARC-EX study (PI: Flatmark) is based on the notion that in the course of tumor growth and possibly by manipulation during the surgical procedure, CRC cells may be shed into the peritoneal cavity and give rise to PC or local recurrences in the pelvic cavity. In a previous study, exfoliated tumor cells were found in lavage fluid from 19 of 237 of LARC patients undergoing surgery, and were associated with poor survival outcome [Kristensen et al., 2008]. The new study started accrual in 2012: The presence of exfoliated tumor cells in peritoneal lavage samples from LARC patients is determined using cancer-specific DNA methylation-based biomarkers [Lind et al., 2011]. Lavage is performed prior to and after manipulation of the tumor during the surgery, to provide data regarding both spontaneous and iatrogenic tumor cell exfoliation and their respective contribution to patient outcome. If exfoliated tumor cells predict tumor recurrence, it would support an active approach to postoperative intraperitoneal chemotherapy.