Primary Peritoneal Cancer, from the CureRays guide library.

Primary peritoneal cancer arises from the lining of the abdomen and behaves much like ovarian cancer; it is treated with surgery and chemotherapy, with radiation reserved for relieving symptoms or treating specific spots.

What it is.

Primary peritoneal cancer is an uncommon cancer that begins in the peritoneum, the thin sheet of tissue that lines the inside of the abdomen and covers the organs within it. Although it forms in the abdominal lining rather than in the ovaries, it closely resembles the most common type of ovarian cancer under the microscope and behaves in very similar ways — which is why it is treated using the same approaches. It can occur in women who still have their ovaries and even in women whose ovaries have been removed, because the peritoneum and the surface of the ovaries share a common origin during development. Because the peritoneum wraps around the abdominal organs, this cancer tends to spread across the surfaces inside the abdomen and to cause a buildup of fluid (ascites), leading to symptoms such as abdominal bloating and swelling, a feeling of fullness, changes in appetite, and abdominal or pelvic discomfort. These symptoms can be vague, so the cancer is often found after it has already spread within the abdomen. A blood marker called CA-125 is often elevated and is used to help with diagnosis and to follow the response to treatment. The mainstays of treatment are surgery to remove as much visible cancer as possible (called debulking or cytoreduction) and chemotherapy, often including modern maintenance medicines and, for some patients, targeted therapies guided by genetic testing such as BRCA status. Radiation has a more limited, supportive role here. Care is led by gynecologic and medical oncologists, with radiation oncologists involved for selected situations.

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 primary peritoneal cancer, radiation has a more limited and supportive role than it does for many other cancers, and it helps to understand why. This cancer spreads diffusely across the broad surfaces inside the abdomen, and treating the entire abdominal lining with radiation would expose large amounts of the intestine, liver, and kidneys to doses they cannot safely tolerate. For that reason, the main treatments are surgery to remove as much cancer as possible and chemotherapy, which can reach cancer throughout the abdomen. Radiation comes into play when there is a specific, localized problem to solve. If a particular spot of cancer is causing pain, bleeding, or pressure — for example a tumor pressing on a structure or a confined area of spread to a lymph node or bone — focused radiation can target that site precisely to relieve the symptom and improve comfort. Modern techniques such as intensity-modulated radiation and stereotactic body radiation therapy shape the dose tightly around a small target while sparing the surrounding sensitive organs, and image guidance keeps each treatment accurate. In selected cases where the cancer is confined to one or a few areas, a high focused dose can provide durable local control. Throughout, radiation is used thoughtfully and in coordination with the gynecologic and medical oncology team, which leads care with surgery, chemotherapy, and maintenance or targeted therapies. Your radiation oncologist helps identify the moments when focused radiation can add meaningful benefit to your overall plan.

The ways we can treat it.

Palliative radiation. Short, focused courses of radiation relieve symptoms from specific tumor sites — such as pain, bleeding, or a localized mass — improving comfort and quality of life.

Stereotactic body radiation therapy (SBRT). Delivers a high, precise dose in a few sessions to a small, well-defined area of cancer, used in selected cases to control a limited spot causing problems.

Targeted radiation to isolated spread. When cancer spreads to a confined site such as a lymph node or bone, focused radiation can control that area while sparing surrounding tissue.

Symptom-directed treatment. Radiation can be aimed at an area causing a blockage or discomfort to ease symptoms when other treatments are not sufficient.

Questions we hear often.

Is primary peritoneal cancer the same as ovarian cancer? They are very closely related. Primary peritoneal cancer begins in the lining of the abdomen rather than the ovaries, but the most common form looks and behaves like high-grade serous ovarian cancer, so it is staged and treated the same way. It can even occur in women whose ovaries have been removed.

Why isn't radiation a main treatment for this cancer? This cancer spreads across the broad surfaces inside the abdomen, and treating the whole abdominal lining with radiation would expose the intestine, liver, and kidneys to unsafe doses. So surgery and chemotherapy, which reach throughout the abdomen, are the mainstays, while radiation is used to target specific spots causing symptoms.

Why does my doctor check CA-125 and BRCA status? CA-125 is a blood marker often elevated in this cancer and is used to help with diagnosis and to follow how well treatment is working. Testing for BRCA and related genetic changes helps predict which medicines — such as PARP inhibitors — are most likely to help, and can have implications for family members.

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