What peritoneal metastases are
The peritoneum is the thin membrane lining the inside of the abdomen and wrapping the organs. When tumour cells break off and implant on it they form scattered nodules: these are peritoneal metastases (also called carcinomatosis). They occur in 5-10 % of colorectal cancers at diagnosis and in more over the course of the disease; they are more common in tumours that perforate the bowel wall, in mucinous and signet-ring cell tumours, and in ovarian involvement of colorectal origin (Krukenberg tumour).
They are hard to see on CT when the nodules are small, so they are sometimes discovered during surgery. They can cause ascites (fluid in the abdomen), bloating, pain or episodes of bowel obstruction. Historically this has been the site with the worst prognosis, because intravenous chemotherapy reaches the peritoneum poorly. That is what surgery tries to change.
How it is measured: the PCI
The abdomen is divided into 13 regions and in each the size of the nodules is scored (0 to 3). The sum is the peritoneal cancer index (PCI), from 0 to 39. The lower, the better: in colorectal cancer surgery is usually offered with a PCI below 15-20; above that, the benefit is lost and the risk is not worth it. The PCI is estimated with CT or MRI, but an exploratory laparoscopy is often needed to measure it properly before deciding on the major operation.
Cytoreductive surgery
It is a long (6-12 hours) and complex operation in which all visible disease is removed: the affected peritoneum (peritonectomies), the omentum and, if necessary, stretches of bowel, the spleen, gallbladder, uterus and ovaries. The aim is complete cytoreduction (CC-0): no visible nodule left behind. That is the factor that most determines the outcome; an operation that leaves macroscopic disease adds little benefit.
Serious complications occur in 20-30 % of those operated on and mortality in expert centres is 1-3 %. Recovery is long: 2-3 weeks in hospital and several months to regain strength; a stoma may be left, sometimes temporary. That is why it is only considered in people in good general health and is done in accredited units with a high volume of cases. In Spain there are reference units in several regions; if your hospital does not have one, ask for a referral.
HIPEC: what it is and what we know
HIPEC (hyperthermic intraperitoneal chemotherapy) consists of, at the end of surgery and still in the operating theatre, washing the abdomen for 30-90 minutes with heated chemotherapy (41-43 °C), with the idea of destroying any microscopic cells left behind. For years it was considered an inseparable part of the treatment.
The French PRODIGE 7 trial put things in perspective: it compared complete cytoreductive surgery with and without oxaliplatin HIPEC in colorectal cancer, and HIPEC did not improve survival (a median of about 41 months in both groups) and increased complications. The conclusion now shared by guidelines is that what cures is the complete surgery; oxaliplatin HIPEC as given in that trial adds nothing. Some centres still use HIPEC with other drugs (mitomycin C) or in other settings, and trials are ongoing; it is reasonable to ask why it is or is not done in your case, and not being offered it is not a sign of worse treatment.
What is clear is that, in well-selected patients, complete cytoreductive surgery achieves median survival of more than 40 months and 15-30 % of patients alive at 5 years, figures unthinkable with chemotherapy alone in this situation.
Systemic chemotherapy and other options
- Intravenous chemotherapy (FOLFOX/FOLFIRI with biological drugs) remains the foundation: before surgery (to select those who respond and do not progress) and/or afterwards. If the disease grows during chemotherapy, surgery no longer makes sense.
- If there are also liver metastases, few and operable, some centres treat both; if there is extensive disease outside the peritoneum, surgery is not done.
- PIPAC (aerosolised chemotherapy by laparoscopy): a technique under study for inoperable disease, to control symptoms or attempt conversion; only within trials or specific programmes.
- Preventive second-look surgery in high-risk patients: trials have not shown benefit, and it is not recommended routinely.
What to ask at your appointment
- What is my estimated PCI, and is a laparoscopy needed to confirm it?
- Has my case been assessed by a reference unit for peritoneal surgery? If not, can you refer me?
- Is complete cytoreduction possible in my case? With what probability and what risks?
- Would HIPEC be done? With which drug and why, given PRODIGE 7?
- Chemotherapy before, after or both? And what if the disease progresses in the meantime?
