Polyclonal peritoneal mets, HIPEC noted
- Conference highlights warned many peritoneal metastases are polyclonal, which complicates single‑target treatments. - Presenters recommended precision strategies including cytoreductive surgery combined with HIPEC for complex peritoneal disease. - Those takeaways were summarized from recent AACR26 social coverage of peritoneal‑disease management and research priorities ( ).
Peritoneal metastases often carry more than one cancer clone, and that is pushing researchers away from one-size-fits-all drug strategies toward tailored combinations and surgery-based care. (aacr.org) The peritoneum is the thin lining of the abdomen, and cancers from the colon, stomach, ovary, pancreas, and appendix can spread there as tumor deposits. In colorectal cancer, the peritoneum is the second most common metastatic site after the liver. (frontiersin.org) A “polyclonal” metastasis means the deposit was seeded by several related cancer cell groups rather than one dominant lineage. Reviews of peritoneal spread now describe multiclonal seeding and note that mixed cell populations can blunt single-target therapies by leaving resistant clones behind. (pmc.ncbi.nlm.nih.gov) That biology has become a practical treatment problem because peritoneal disease already behaves differently from cancer in the liver or lung. Systemic drugs also penetrate the peritoneal cavity less efficiently, which is one reason surgery and regional chemotherapy remain central in selected patients. (pmc.ncbi.nlm.nih.gov) The surgery is called cytoreductive surgery, or CRS, and the goal is to remove every visible tumor implant in the abdomen. Hyperthermic intraperitoneal chemotherapy, or HIPEC, bathes the abdominal cavity with heated chemotherapy during the operation to treat microscopic disease that surgeons cannot see. (pmc.ncbi.nlm.nih.gov) Who gets CRS and HIPEC depends heavily on selection. Recent reviews and guidelines point to the Peritoneal Cancer Index, a score that maps tumor burden across the abdomen, and to whether a complete cytoreduction is realistically achievable. (frontiersin.org) The evidence is still unsettled on exactly when HIPEC adds benefit, and recent consensus guidance says the overall literature base remains low quality in several decision points. A 2025 Delphi guideline for colorectal peritoneal metastases recommended early referral to a peritoneal surface malignancy center and de-emphasized upfront cytoreductive surgery for synchronous disease in favor of systemic therapy first. (link.springer.com) Trials are still testing how to combine these tools. The CAIRO6 study, listed as active and not recruiting as of March 24, 2026, randomizes patients with isolated resectable colorectal peritoneal metastases to perioperative systemic therapy plus CRS-HIPEC or to upfront CRS-HIPEC alone. (clinicaltrials.gov) Researchers are also trying to make HIPEC itself more precise. A 2026 study in *Annals of Surgical Oncology* reported that colorectal peritoneal metastases are enriched for the consensus molecular subtype called CMS4 and argued that subtype information may help choose intraperitoneal agents. (pubmed.ncbi.nlm.nih.gov) Those are the stakes behind the AACR 2026 discussion in San Diego from April 17 to 22: peritoneal metastases are not one uniform target, and treatment plans are increasingly being built around clone diversity, tumor burden, and whether complete surgery is possible. (aacr.org)
