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What is primary peritoneal cancer?
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.
The main types
Doctors group primary peritoneal cancer by where it starts and how it behaves:
| Type | What it means, simply |
|---|---|
| Serous primary peritoneal carcinoma | By far the most common form; looks and behaves like high-grade serous ovarian cancer and is treated the same way, with surgery and chemotherapy. |
| Primary peritoneal mesothelioma | A distinct, rarer cancer of the peritoneal lining (different from the serous type), sometimes linked to asbestos, treated with specialized surgery and chemotherapy approaches. |
Staging, in plain terms
Primary peritoneal cancer is staged with the FIGO system, the same one used for ovarian and fallopian-tube cancers, because these cancers are so similar in behavior. Rather than the TNM letters, FIGO uses stages I through IV based on how far the cancer has spread within and beyond the abdomen. Because primary peritoneal cancer arises from the abdominal lining itself and tends to spread across the surfaces inside the abdomen, it is most often diagnosed at a more advanced stage — typically stage III or IV — where cancer is found on the surfaces of abdominal organs or beyond. Stage III generally means the cancer has spread across the lining of the abdomen or to lymph nodes in the area, while stage IV means it has spread to more distant sites, such as inside the liver, the lungs, or fluid around the lungs. The amount of cancer remaining after surgery is one of the most important factors for the outlook: removing all or nearly all visible disease (an optimal debulking) is associated with better results. Doctors also use the CA-125 blood marker and genetic testing (such as BRCA status) to guide treatment and follow-up, since these influence which medicines are most likely to help.
| FIGO staging (shared with ovarian/fallopian-tube cancer) | What it generally means |
|---|---|
| Stage I–II (uncommon) | Cancer limited to a confined area within the pelvis; uncommon for this cancer, treated with surgery and chemotherapy. |
| Stage III | Cancer that has spread across the lining of the abdomen or to nearby lymph nodes; treated with surgery to remove as much as possible plus chemotherapy. |
| Stage IV | Cancer that has spread to more distant sites such as inside the liver, the lungs, or fluid around the lungs; treated with chemotherapy, surgery in selected cases, and maintenance or targeted therapy. |
The standard of care
Primary Peritoneal Cancer 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:
Surgery (cytoreduction / debulking)
An operation removes as much visible cancer as possible from the abdomen; the more completely the cancer is removed, the better the outlook, making expert surgery a cornerstone of treatment.
Chemotherapy
Chemotherapy, often a platinum-based combination, is central to treatment and may be given before surgery to shrink the cancer, after surgery, or both; it is the same approach used for ovarian cancer.
Maintenance and targeted therapy
After initial treatment, medicines such as PARP inhibitors (especially helpful when a BRCA change is present) and other targeted or anti-blood-vessel drugs can lengthen the time the cancer stays controlled.
Genetic testing
Testing the tumor and sometimes the patient for changes such as BRCA helps predict response to certain medicines and has implications for family members.
Radiation for selected situations
Radiation is not a routine part of treatment but can relieve symptoms — such as pain or bleeding from a specific spot — or target a localized area of cancer that is causing problems.
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 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 main ways radiation is delivered for primary peritoneal cancer:
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.
Latest studies shaping care
Care keeps improving — often toward getting the same excellent results with less burden on patients. A few developments:
PARP inhibitors extend control, especially with BRCA changes: Trials showed that maintenance PARP inhibitor medicines lengthen the time the cancer stays controlled after chemotherapy, with the greatest benefit in patients whose tumors carry BRCA or related genetic changes — the same advances driving ovarian cancer care.[1]
Maintenance PARP inhibitor trials
Complete surgical removal improves outcomes: Research consistently found that removing all or nearly all visible cancer during surgery is one of the strongest predictors of a good outcome, underscoring the value of expert surgical care.[2]
Cytoreduction outcome studies
Stereotactic radiation for limited spread: Studies support using focused stereotactic radiation to control isolated areas of cancer causing symptoms or limited spread, providing precise local control while sparing nearby organs.[3]
Oligometastatic SBRT analyses
Common questions
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.
References
Numbered sources for the studies cited above. Links open the primary publication on PubMed or the publisher’s site.