Peritoneal metastases

Published by the practice of Charalambos Charalambous, MD, ChM, General Surgeon, German Medical Institute, Limassol, Cyprus. Last updated: 19 September 2026.

Peritoneal metastases are deposits of cancer on the lining of the abdominal cavity. For most of the twentieth century this was regarded as a terminal finding and treated only with palliative intent. That position has changed for selected patients. It is now understood that peritoneal spread from certain tumours behaves as regional disease rather than as systemic dissemination, and for a defined group of patients, treatment combining complete surgical removal of visible disease with chemotherapy delivered directly into the abdomen offers long-term survival and occasionally cure. The essential clinical task is identifying which patients fall into that group — and being honest with those who do not.

How they form

The peritoneum is a continuous membrane lining the abdominal cavity and covering its organs, with a surface area comparable to that of the skin. It is lined by a single layer of mesothelial cells over a basement membrane and connective tissue containing lymphatics and blood vessels.

The process of peritoneal spread — the "seed and soil" sequence — unfolds in defined steps:

1. Detachment. Tumour cells lose their adhesion to one another, typically through loss of E-cadherin, and separate from the primary tumour. This happens once a tumour breaches the serosal surface of the organ it arose in, or through spillage at surgery or perforation.
2. Transport. Free cells circulate in peritoneal fluid, carried by gravity and by the currents created by diaphragmatic movement and peristalsis. This is why deposits accumulate in predictable places: the pelvis (the lowest point), the right subphrenic space, the greater omentum, and along the paracolic gutters.
3. Attachment. Cells adhere to the mesothelium via adhesion molecules, or lodge preferentially where the mesothelium is naturally interrupted — the milky spots of the omentum, which are lymphatic-rich openings designed for immune surveillance and which function as ready-made landing sites.
4. Invasion and growth. Cells retract the mesothelium, invade the underlying connective tissue, and recruit a blood supply.
5. Ascites. Deposits obstruct the lymphatic stomata of the diaphragm through which peritoneal fluid normally drains, while also increasing capillary permeability through VEGF. Fluid accumulates.

Surgery itself contributes: a peritoneal surface stripped of mesothelium exposes basement membrane to which free tumour cells adhere far more readily. This is the rationale for giving intraperitoneal chemotherapy at the time of surgery, when free cells are present and adhesion has not yet occurred.

Which cancers do this

• Colorectal cancer — a substantial proportion of patients, particularly with T4 tumours, perforation, or mucinous histology
• Gastric cancer — especially diffuse-type, where peritoneal spread is the dominant pattern of failure
• Ovarian cancer — where peritoneal spread is the natural history of the disease
• Appendiceal tumours — including mucinous neoplasms causing pseudomyxoma peritonei, covered separately
• Pancreatic and biliary cancer
• Peritoneal mesothelioma — a primary rather than secondary tumour, covered separately

Symptoms

Early disease causes nothing, which is why it is often found at surgery for another purpose or on staging laparoscopy. Later features:

• Abdominal distension from ascites, often the first noticed symptom
• abdominal pain, typically vague and diffuse
• early satiety and reduced appetite
• weight loss, with the paradox of a distended abdomen and wasted limbs
• nausea, vomiting, and intermittent or complete bowel obstruction from deposits encasing bowel loops
• breathlessness from diaphragmatic splinting
• an umbilical nodule (Sister Mary Joseph nodule)
• fatigue, and in some cases deep vein thrombosis

How the diagnosis is made

• CT of chest, abdomen and pelvis — the standard, showing ascites, omental thickening ("omental cake"), peritoneal nodules and stranding. Its important limitation, which must be stated: CT substantially underestimates the extent of peritoneal disease, particularly small-volume disease and involvement of the small bowel and its mesentery, which is precisely what determines whether complete removal is possible.
• MRI with diffusion-weighted imaging — more sensitive for small-volume peritoneal disease and increasingly used when cytoreductive surgery is being considered.
• PET-CT — useful for non-mucinous tumours; unreliable for mucinous disease, which is not metabolically avid.
• Diagnostic laparoscopy — the most accurate assessment of extent and resectability, and essential before committing a patient to major surgery. It allows direct inspection of the small bowel and mesentery, biopsy, and calculation of the Peritoneal Cancer Index (PCI), which divides the abdomen into thirteen regions and scores the size of deposits in each, giving a total from 0 to 39.
• Ascitic fluid cytology — confirms malignancy where positive, but a negative result does not exclude it.
• Tumour markers — CEA, CA 19-9, CA 125, with trends more informative than single values.

Treatment

Selecting patients — the central question

Cytoreductive surgery with intraperitoneal chemotherapy is a major undertaking, and offering it to the wrong patient does harm. The factors that determine suitability:

• Can all visible disease be removed? This is the single most important determinant of outcome. Survival benefit is confined almost entirely to patients in whom complete or near-complete cytoreduction is achieved.
• Extent of disease (PCI) — thresholds differ by tumour. For colorectal disease, benefit falls off substantially above a PCI of around 20; for pseudomyxoma, even very extensive disease may be treatable.
• Small bowel and mesenteric involvement — extensive involvement usually makes complete removal impossible, since the small bowel cannot be sacrificed.
• Tumour biology — histology, grade, mutation status, and response to systemic chemotherapy. A tumour progressing on chemotherapy is unlikely to be served by major surgery.
• Absence of significant disease outside the abdomen.
• Patient fitness — this is a long operation with substantial physiological demand.

Cytoreductive surgery (CRS)

The aim is removal of all macroscopic disease, by a combination of peritonectomy procedures — stripping the parietal peritoneum from the abdominal wall, diaphragm and pelvis — and resection of involved organs: omentum, spleen, gallbladder, segments of bowel, and parts of the stomach or other organs as required. It is typically an eight to twelve hour operation.

Hyperthermic intraperitoneal chemotherapy (HIPEC)

Chemotherapy heated to around 41–43°C is circulated through the abdominal cavity at the end of the operation, for thirty to ninety minutes. The rationale is pharmacological: the peritoneal-plasma barrier keeps drug concentrations in the abdomen many times higher than in the blood, limiting systemic toxicity; heat is directly cytotoxic, increases drug penetration into tissue, and acts synergistically with several agents. It is given while free tumour cells are present and before adhesions form.

The honest position on HIPEC: its benefit is well established in pseudomyxoma peritonei and peritoneal mesothelioma, and supported in ovarian cancer in defined settings. In colorectal peritoneal metastases the PRODIGE 7 trial found that adding oxaliplatin HIPEC to complete cytoreductive surgery did not improve survival — a result that prompted genuine reappraisal. The current understanding is that the survival benefit comes principally from complete cytoreduction, with the role and choice of HIPEC agent still being defined. Patients deserve this nuance rather than an oversold account.

Other approaches

• Systemic chemotherapy and targeted therapy — the mainstay for most patients, and used before and after cytoreductive surgery in those selected for it.
• PIPAC (pressurised intraperitoneal aerosol chemotherapy) — chemotherapy delivered as an aerosol at laparoscopy, repeated at intervals. Palliative and investigational, used for disease too extensive for cytoreduction, with promising results in controlling ascites and symptoms.
• Palliative measures — paracentesis or an indwelling drain for ascites; stenting, bypass or a venting gastrostomy for obstruction; nutritional support; and early specialist palliative care, which improves both quality of life and, in some settings, survival.

Recovery

Cytoreductive surgery with HIPEC is one of the largest operations in general surgery. Hospital stay is typically two to three weeks, usually including critical care. Complications occur in a significant proportion — anastomotic leak, fistula, bleeding, infection, renal and haematological toxicity — and mortality, while low in high-volume centres, is not negligible. Recovery to full activity takes three to six months.

This is why the operation is performed only in specialist centres with the necessary critical care, radiology and oncology support, and why patient selection is discussed at length rather than assumed.

Follow-up

Regular clinical review, tumour markers and CT, with MRI where CT is uninformative. Recurrence is common and may itself be treatable in selected cases.

When to seek an opinion

A patient found to have peritoneal deposits — at operation, on a scan, or from ascitic fluid — should be discussed with a specialist peritoneal malignancy centre before being told that only palliative treatment is available. The judgement about resectability is a specialist one, and a proportion of patients told there is nothing to be done prove to be candidates for treatment with curative intent.

Common questions

Does this mean the cancer has spread everywhere?

Not necessarily. Spread to the lining of the abdomen behaves differently from spread through the bloodstream to distant organs. For certain cancers it is regarded as regional rather than widespread disease, and if it can all be removed, long-term survival is possible. Whether that applies to you depends on the type of cancer and how extensive the deposits are.

What is HIPEC and does it work?

It is heated chemotherapy circulated through the abdomen at the end of the operation, so the drug reaches the surfaces directly at a much higher concentration than would be safe to give into a vein. It is well established for some conditions, particularly pseudomyxoma and mesothelioma. For bowel cancer, a major trial found that the benefit comes principally from removing all the visible disease rather than from the heated chemotherapy itself. You deserve a straight account of which situation applies to you.

How do you decide whether I am suitable for surgery?

The decisive question is whether every visible deposit can be removed, because the benefit is almost entirely confined to patients where that is achieved. This depends on how much disease there is, where it sits — particularly whether the small bowel and its supporting tissue are extensively involved — how the cancer has behaved on chemotherapy, and how fit you are for a long operation. A laparoscopy is often the only way to answer it reliably, because scans underestimate the extent.

Why do scans not show it accurately?

Because the deposits can be very small and spread over a large surface, and the small bowel moves and folds, hiding disease. CT routinely underestimates the extent, which is why a camera inspection is often needed before committing to a major operation, and why the findings at operation sometimes differ from the scan.

How big an operation is it?

Substantial — commonly eight to twelve hours, with a hospital stay of two to three weeks, usually including intensive care, and three to six months before you feel fully recovered. Complications are not rare. This is why it is done only in specialist centres and why the decision is weighed so carefully.

My abdomen keeps filling with fluid. What can be done?

The fluid can be drained, and where it recurs quickly a small permanent drain can be placed so that it can be managed at home rather than through repeated hospital visits. Chemotherapy, and in some centres aerosolised chemotherapy given at laparoscopy, can reduce the rate at which it forms. This is worth addressing actively, as it is one of the most burdensome symptoms.

I have been told nothing can be done. Is that necessarily true?

It may be, but it is worth a second opinion from a centre specialising in this. Assessing whether complete removal is possible is a specialist judgement, and a proportion of patients told that only palliative treatment is available turn out to be candidates for treatment aimed at long-term control. Asking for that referral is entirely reasonable.

Related conditions

Other conditions of the peritoneal disease covered on this site:

• Pseudomyxoma peritonei
• Peritoneal mesothelioma
• Primary peritoneal cancer
• Peritonitis
• Intra-abdominal abscess
• Adhesions and adhesive bowel obstruction

This page provides general information and does not replace an individual medical consultation. Assessment and treatment are decided for each patient after review of their history, examination, investigations and discussion in a specialist multidisciplinary meeting.