Peritoneal Mesothelioma, from the CureRays guide library.

Peritoneal mesothelioma is a rare cancer of the lining of the abdomen; the main treatment is specialized surgery to remove visible tumor combined with heated chemotherapy bathed directly in the abdomen, with systemic therapy and, occasionally, targeted radiation for symptom relief.

What it is.

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.

How radiation treats it.

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 ways we can treat it.

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.

Questions we hear often.

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.

This guide is informational only. It is not medical advice — please confirm anything here with your care team.