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What is peritoneal mesothelioma?
Peritoneal mesothelioma is a rare cancer that begins in the peritoneum, the thin membrane that lines the inside of the abdomen and covers the organs within it. It is a distinct disease from the more familiar pleural mesothelioma, which arises in the lining of the lungs, although both are linked to past asbestos exposure (the abdominal form less consistently so). Because the peritoneum wraps around the abdominal organs, this cancer tends to spread along surfaces throughout the abdomen rather than forming a single lump, and it often causes vague symptoms that build slowly — abdominal swelling and fluid buildup, belly pain, bloating, a feeling of fullness, weight loss, or changes in bowel habits. These symptoms can be mistaken for other conditions, so diagnosis is sometimes delayed. Doctors evaluate it with imaging such as CT or MRI, often a sample of the abdominal fluid or a biopsy, and specialized pathology to confirm the type. The encouraging news is that, unlike many advanced abdominal cancers, peritoneal mesothelioma that is confined to the abdomen can often be treated with intent to control it for years through a specialized combined approach. Because it is rare and treatment is highly specialized, care at an experienced center is especially important.
The main types
Doctors group peritoneal mesothelioma by where it starts and how it behaves:
| Type | What it means, simply |
|---|---|
| Epithelioid peritoneal mesothelioma | The most common type and the one with the most favorable outlook; it responds best to the specialized surgery-plus-heated-chemotherapy approach. |
| Biphasic peritoneal mesothelioma | A mix of epithelioid and sarcomatoid features; behavior and outlook fall between the two pure types, and treatment is individualized. |
| Sarcomatoid peritoneal mesothelioma | A less common, more aggressive type that is harder to treat and more often managed with medication-based therapy. |
| Well-differentiated papillary and multicystic forms | Rare, low-grade or borderline tumors of the peritoneum that grow slowly and are usually managed with surgery, with a generally favorable outlook. |
Staging, in plain terms
Because peritoneal mesothelioma spreads across surfaces throughout the abdomen rather than forming one tumor, doctors measure it differently from many cancers. A formal TNM stage exists, but in practice the most useful guide is how much tumor is present and how widely it is distributed across the abdominal cavity. Surgeons often use a score called the Peritoneal Cancer Index, which divides the abdomen into regions and rates how much tumor is in each, giving a number that reflects the overall burden of disease. They also judge whether the tumor can be removed surgically — described by how 'complete' a cytoreduction (removal of visible tumor) can be achieved — because the chance of long-term control is closely tied to removing as much disease as possible. Other important factors include the tumor's type under the microscope (epithelioid types do best) and whether disease has spread outside the abdomen, which is uncommon. Rather than a single number driving everything, the team weighs the extent and distribution of tumor, its biology, and whether complete surgical removal is feasible to decide on the best treatment.
| Peritoneal Cancer Index and TNM (extent of tumor spread across the abdomen) rather than a simple lump size | What it generally means |
|---|---|
| Limited, removable disease | Tumor is confined to the abdomen and spread is limited enough that a surgeon can remove all or nearly all visible disease; this is the situation best suited to the specialized surgery-plus-heated-chemotherapy approach with the goal of long-term control. |
| Extensive abdominal disease | Widespread tumor throughout the abdomen that cannot be completely removed by surgery; treatment focuses on systemic medication and relieving symptoms, with surgery considered only in selected cases. |
| Disease spread outside the abdomen | Uncommon spread beyond the abdominal cavity; treatment centers on systemic therapy, with targeted radiation or other measures used to relieve specific symptoms. |
The standard of care
Peritoneal Mesothelioma is almost always treated by a team that may include a surgeon, a medical oncologist, and a radiation oncologist, combining therapies for the best result. The usual building blocks are:
Cytoreductive surgery (CRS)
A specialized, often lengthy operation to remove all visible tumor from the abdominal surfaces and organs. Achieving a complete removal is the single most important factor for long-term control.
Heated intraperitoneal chemotherapy (HIPEC)
Immediately after surgery, warmed chemotherapy is circulated directly inside the abdomen to destroy microscopic tumor cells the surgeon cannot see. Combining HIPEC with complete surgery is the cornerstone treatment for suitable patients.
Systemic chemotherapy and targeted therapy
Medication that travels through the bloodstream is used for disease that cannot be fully removed, before or after surgery in some cases, or for more aggressive types.
Immunotherapy and clinical trials
Because the disease is rare, newer immune-based treatments and trials are an important option, especially for disease that is not suitable for surgery.
Supportive care
Draining abdominal fluid, managing pain and nutrition, and relieving blockages help patients feel and function better throughout treatment.
How radiation treatment works
Radiation therapy uses focused high-energy beams to damage the DNA inside cancer cells so they can no longer grow and divide. For most cancers that stay in one place, radiation can be aimed precisely at the tumor, but peritoneal mesothelioma poses a special problem: it spreads as a thin coating across the surfaces lining the entire abdomen, and the organs there — the small and large bowel, liver, and kidneys — cannot safely tolerate radiation across such a wide area. For that reason, radiation is not the main treatment. Instead, the job of treating the whole abdominal surface is done by surgery to remove visible tumor combined with heated chemotherapy circulated directly inside the abdomen, which reaches the surfaces a beam cannot safely cover. Radiation still has a supporting role. It can be aimed at a single troublesome spot — for example, an area causing pain — to provide relief, and it is sometimes directed at surgical scar or drain sites where mesothelioma can occasionally seed, to discourage tumor from growing there. When radiation is used, modern planning with intensity-modulated techniques shapes the dose tightly around the target to protect nearby healthy organs. Your care team decides whether radiation has a role in your situation based on where the disease is and what symptoms it is causing, always weighing benefit against the sensitivity of the surrounding organs.
The main ways radiation is delivered for peritoneal mesothelioma:
Targeted (palliative) external-beam radiation
Radiation is not a primary treatment for peritoneal mesothelioma because the disease is spread across the abdomen and the surrounding organs cannot tolerate whole-abdomen radiation. It is used selectively to shrink a specific painful or problematic area and relieve symptoms.
Radiation to prevent or treat tumor at incision sites
In some cases, focused radiation is directed at surgical scar or drain sites where mesothelioma can occasionally seed, to reduce the chance of tumor growing there.
Why whole-abdomen radiation is not used
Delivering radiation to the entire abdominal lining would expose the bowel, liver, and kidneys to unsafe doses, so the heated chemotherapy bath (HIPEC) — not radiation — is the tool used to treat the whole abdominal surface.
Latest studies shaping care
Care keeps improving — often toward getting the same excellent results with less burden on patients. A few developments:
Multisociety consensus reinforces surgery plus HIPEC: A 2025 multisociety consensus effort strengthened the recommendation for cytoreductive surgery combined with heated intraperitoneal chemotherapy as the standard for diffuse malignant peritoneal mesothelioma that can be surgically removed.[1]
PSOGI multisociety consensus (2025)
Long-term survival after complete cytoreduction and HIPEC: Series from specialized centers report median survival of several years and 5-year survival approaching half of patients when complete surgical removal is achieved and combined with heated chemotherapy, far better than historical outcomes.[2]
Cytoreduction and HIPEC outcome studies
Immunotherapy expands options for inoperable disease: Immune-based therapies are being studied and used for mesothelioma that cannot be surgically removed, offering additional options for patients beyond traditional chemotherapy.[3]
Mesothelioma immunotherapy trials
Common questions
Is this the same as the mesothelioma that affects the lungs? No. Peritoneal mesothelioma arises in the lining of the abdomen, while pleural mesothelioma arises in the lining of the lungs. They are related but distinct diseases with different treatments. The abdominal form is often treated with specialized surgery plus heated chemotherapy and can frequently be controlled for years when caught while confined to the abdomen.
Why isn't radiation the main treatment? Because the cancer coats surfaces across the entire abdomen, and the bowel, liver, and kidneys cannot safely tolerate radiation over such a wide area. The whole-abdomen job is done instead by surgery plus heated chemotherapy. Radiation is reserved for relieving a specific painful spot or treating surgical scar sites.
What makes the biggest difference in outcome? Whether a surgeon can remove all or nearly all of the visible tumor, combined with heated chemotherapy, is the strongest factor for long-term control. The tumor's type also matters — the epithelioid type does best. Because this is rare and highly specialized, treatment at an experienced center is important.
References
Numbered sources for the studies cited above. Links open the primary publication on PubMed or the publisher’s site.