What are HIPEC and PIPAC for cancer that has spread to the peritoneum?

HIPEC and PIPAC are two different ways of delivering medication into the abdominal cavity for cancer that has spread to the peritoneum. In HIPEC, a heated solution of cancer-fighting drugs is usually circulated through the abdomen after visible tumours have been removed. This drug treatment is called chemotherapy. In PIPAC, the drug is sprayed under pressure as fine droplets. Their uses, aims and the evidence for their benefits are not the same.

Suitability is assessed individually. The decision depends on where the cancer started, how far it has spread within the abdomen, whether the visible tumours can be removed and the person's general condition, so these treatments are not offered to every patient and do not guarantee a cure. In particular, researchers are still investigating which patients benefit from PIPAC and to what extent.

What does peritoneal carcinomatosis mean?

The peritoneum is a thin membrane that lines the inside of the abdominal wall and covers much of the surface of the abdominal organs. When cancer cells from another organ form deposits on this surface, this is called peritoneal carcinomatosis or peritoneal metastases. Metastasis means cancer has spread from where it started to another area. Peritonitis, by contrast, is inflammation of the membrane. These are different conditions.

This type of spread can occur with tumours originating in the colon, stomach, ovaries and appendix, the worm-shaped extension of the bowel. Treatment is not chosen solely according to the site of spread. For example, although cancer starting in the stomach and a tumour starting in the appendix may both appear on the peritoneum, their behaviour and treatment options can differ.

Abdominal swelling, feeling full quickly, pain and changes in bowel habits may occur. A build-up of fluid in the abdominal cavity is called ascites; it causes the abdomen to enlarge and can sometimes make breathing uncomfortable. In some people, however, peritoneal deposits are found during another investigation.

Computed tomography, which produces cross-sectional images of the body, helps assess the extent of spread. Small deposits may not be visible. An examination inside the abdomen with a camera and tissue sampling may then be needed. The surgical team considers both the number of deposits and where they are located, particularly any spread along the small intestine.

Tumour removal and HIPEC are separate stages

The aim of cytoreductive surgery is to remove visible tumour deposits. This may require removal of parts of the peritoneum and sometimes parts of organs affected by the disease. If a section of bowel is also removed, its ends may need to be joined, or a stoma may be needed, in which the bowel is brought out through the abdominal wall to allow stool to pass. These possibilities are discussed before surgery.

HIPEC is the drug treatment stage of that operation. A heated chemotherapy solution is circulated through the abdominal cavity and then removed. The aim is to treat microscopic cells that may remain on the surfaces. The drug does not replace surgical removal of large visible tumour deposits, nor does it automatically replace systemic drug treatment for cancer that has spread outside the abdomen.

There is a stronger basis for considering potential benefit from surgery in selected cases where visible disease can be removed completely or to the required extent. Extensive involvement of the small intestine, deposits that cannot be removed and an inability to tolerate major surgery may limit this option. Spread outside the abdomen is also considered separately.

Which patients may benefit?

HIPEC results from one type of cancer cannot be applied to another. Disease involving a build-up of mucus on the peritoneum from some appendix tumours, along with certain other conditions, is assessed for this approach by a specialist team. In a specific group of patients with ovarian cancer, adding HIPEC to surgery after initial chemotherapy has been shown to provide benefit. This does not apply to everyone.

In selected cases of colon cancer that has spread only to the peritoneum, surgical removal of the tumours may be discussed. However, the additional benefit of adding HIPEC to surgery is less certain. In a large comparative study, HIPEC using a drug called oxaliplatin did not improve survival, and some later complications were more frequent. A separate explanation is therefore needed for the choice of drug and how it will be given.

This combination also cannot be described as a general standard treatment for stomach cancer that has spread to the peritoneum. Comparative studies have not consistently shown a survival benefit from adding surgery and HIPEC to drug treatment, so any proposal should clearly explain its aim, the available evidence and whether it is part of a research study.

The surgeon and oncologist decide on suitability together, based on imaging, tissue results, response to previous treatment and organ function. Age alone does not determine the decision. Nutritional deficiencies, mobility, kidney function and heart function help weigh the potential benefit of major surgery against its burden.

Why is PIPAC being investigated?

PIPAC is delivered during laparoscopy, using a camera and instruments inserted through small abdominal incisions. A special device turns liquid chemotherapy into an aerosol of very fine droplets and delivers it into the abdominal cavity. This is not an inhaled medicine. The procedure is performed under anaesthesia, and repeat sessions may be planned in selected protocols.

This approach is being investigated in some patients for whom extensive surgical removal of tumours is unsuitable. The aim may be to control the disease and reduce symptoms, but there is not yet enough high-quality evidence about its effects on survival and quality of life. Because PIPAC is not considered a proven curative treatment suitable for everyone, patients must be told about the research setting, the uncertainty of the expected benefit and the available alternatives before giving consent.

The video showing PIPAC alongside stomach surgery contains surgical footage intended for adults. It shows one particular procedure and does not demonstrate that this combination is suitable for all patients with stomach cancer. The techniques are also presented on the surgery for peritoneal carcinomatosis page.

Risks and treatment of day-to-day symptoms

Extensive surgery can involve bleeding, infection, leakage from a bowel join and a long recovery period. Chemotherapy can affect the kidneys and blood cells. Small incisions do not eliminate risk. Bowel injury, pain and drug-related complications can occur with PIPAC, while adhesions from previous operations sometimes prevent the procedure by making safe access to the abdomen impossible.

When these procedures are unsuitable, a plan is made for pain relief, nutritional support, drainage of fluid that has collected in the abdomen and cancer drug treatment. Relieving symptoms is a treatment goal in its own right and can be pursued alongside medicines that treat the disease.

Increasing abdominal pain, repeated vomiting and an inability to pass wind or stool may indicate bowel obstruction and require urgent assessment. Severe breathlessness, altered consciousness and fever after a procedure also need prompt attention. Gradual abdominal enlargement, eating less and weight loss should be reported to the treatment team so that the support plan can be adjusted in good time.