Conversion surgery after repeated intraperitoneal chemotherapy in unresectable peritoneal metastatic colorectal cancer: a narrative review of the literature.

Peritoneal metastases from colorectal cancer (CRC-PM) are known to respond poorly to systemic chemotherapy. Therefore, in patients with irresectable CRC-PM, treatments with repeated administration of intraperitoneal chemotherapy via pressurized intraperitoneal aerosol chemotherapy (PIPAC) or catheter-based intraperitoneal chemotherapy (CBIPC) have been introduced. Currently, it is unknown whether such palliative-intent therapy may play a role in converting patients with irresectable CRC-PM into candidates for cytoreductive surgery (CRS). The current study reviewed all literature available up to 1st December 2025 investigating palliative intraperitoneal therapies in patients diagnosed with CRC-PM. Inclusion of articles was further based on the availability of conversion surgery data. Data on safety, response and survival outcomes were also collected. In total, 14 studies on PIPAC and 4 studies on CBIPC were included. Conversion to CRS rates after bidirectional treatment in retrospective studies were up to 27% with PIPAC-Oxaliplatin and to 34% with CBIPC-Paclitaxel. In clinical trials, a conversion rate of 17% and 22% were found respectively after PIPAC-Oxaliplatin monotherapy and CBIPC-Irinotecan plus systemic therapy. Outcomes after conversion surgery are rarely reported. Repetitive intraperitoneal chemotherapy was found to enable conversion to CRS in part of the patients with irresectable CRC-PM. Though promising, the current review highlights the heterogeneity of data on palliative intraperitoneal therapies in irresectable CRC-PM, hampering the intra- and across modality comparison of results. Further research is needed to indicate the optimal delivery system, intraperitoneal agent, timing of treatment initiation, number of cycles and bimodality.