Colorectal peritoneal metastases: pathogenesis, diagnosis and treatment options - an evidence-based update.

Peritoneal metastases confer the worst survival among all sites in patients with metastatic colorectal cancer. They develop largely through transcoelomic spread, with a sequence of events that allow cells to first detach from primary tumours, survive in the peritoneal environment, attach to the peritoneal surface of organs and migrate into the submesothelial space to create a microenvironment conducive to metastatic growth. Diagnostic challenges have previously hindered early identification of peritoneal metastases. While advances in diagnostic modalities have improved our ability to identify peritoneal metastases, lesions under 0.5 cm remain challenging to detect. The advent of cytoreductive surgery with hyperthermic intraperitoneal chemotherapy (HIPEC) can offer selected patients with colorectal peritoneal metastases a favourable long-term survival. Recent trials, however, have cast doubts on the efficacy of HIPEC, with the recent PRODIGE 7 trial showing no benefit from oxaliplatin based HIPEC in addition to good quality cytoreductive surgery in resectable disease. While peritoneal recurrence can be reliably predicted from high-risk features in primary tumours such as a perforated cancer, ovarian metastases or T4a cancers, the use of prophylactic second look surgery with HIPEC or adjuvant HIPEC failed to demonstrate any survival benefit in high-risk cases in recent clinical trials, raising further questions about the efficacy of HIPEC. With high failure rates from systemic chemotherapy in unresectable disease, novel surgical techniques such as pressurized intraperitoneal aerolized chemotherapy are being investigated in clinical trials worldwide. Further collaborative research is needed to explore newer avenues of treatment for this poor prognostic cohort.