Peritoneal cancer is a rare cancer that forms in the thin layer of epithelial cells that line the inside wall of the abdomen. This lining is called the peritoneum.
The peritoneum protects and covers the organs in your abdomen, including the:
The peritoneum also produces a lubricating fluid that allows the organs to move easily inside the abdomen.
Because its symptoms most often go undetected, peritoneal cancer is usually diagnosed at a late stage.
Each case of peritoneal cancer is different. Treatment and outlook vary individually. New treatments developed in the last decades have improved survival rates.
Primary vs. secondary peritoneal cancer
The designations of primary and secondary refer to where the cancer started. The names aren’t a measure of how serious the cancer is.
Primary peritoneal cancer starts and develops in the peritoneum. It usually only affects women and very rarely affects men.
Primary peritoneal cancer is closely related to epithelial ovarian cancer. Both are treated the same way and have a similar outlook.
A rare type of primary peritoneal cancer is peritoneal malignant mesothelioma.
Secondary peritoneal cancer usually starts in another organ in the abdomen and then spreads (metastasizes) to the peritoneum.
Secondary peritoneal cancer can start in the:
- fallopian tubes
- small bowel
Secondary peritoneal cancer can affect both men and women. It’s more common than primary peritoneal cancer.
Doctors estimate between 15 and 20 percent of people with colorectal cancer will develop metastases in the peritoneum. Around 10 to 15 percent of people with stomach cancer will develop metastases in the peritoneum.
When the cancer metastasizes from its original site, the new site will have the same type of cancer cells as the initial site.
Symptoms of peritoneal cancer
Symptoms of peritoneal cancer depend on the type and stage of the cancer. In its early stages, there may be no symptoms. Sometimes even when the peritoneal cancer is advanced there may be no symptoms.
Early symptoms can be vague and possibly caused by many other conditions. Symptoms of peritoneal cancer can include:
- abdominal bloating or pain
- enlarged abdomen
- a feeling of pressure in the abdomen or pelvis
- fullness before you finish eating
- nausea or vomiting
- bowel or urinary changes
- loss of appetite
- weight loss or weight gain
- vaginal discharge
- back pain
As the cancer progresses, a watery fluid can accumulate in the abdominal cavity (ascites), which can cause:
- nausea or vomiting
- shortness of breath
- stomach pain
Symptoms of late-stage peritoneal cancer can include:
- complete bowel or urinary blockage
- stomach pain
- inability to eat or drink
Stages of peritoneal cancer
When it’s first diagnosed, peritoneal cancer is staged according to its size, position, and where it’s spread from. It’s also given a grade, which estimates how quickly it’s able to spread.
Primary peritoneal cancer
Primary peritoneal cancer is staged with the same system used for ovarian cancer since the cancers are similar. But primary peritoneal cancer is always classed as stage 3 or stage 4. Ovarian cancer has two earlier stages.
Stage 3 is divided into three further stages:
- 3A. The cancer has spread to lymph nodes outside the peritoneum, or cancer cells have spread to the surface of the peritoneum, outside the pelvis.
- 3B. The cancer has spread to the peritoneum outside the pelvis. The cancer in the peritoneum is 2 centimeters (cm) or smaller. It may have also spread to lymph nodes outside the peritoneum.
- 3C. The cancer has spread to the peritoneum outside the pelvis and. The cancer in the peritoneum is larger than 2 cm. It may have spread to lymph nodes outside the peritoneum or to the surface of the liver or spleen.
In stage 4, cancer has spread to other organs. This stage is further divided:
- 4A. Cancer cells are found in the fluid that builds up around the lungs.
- 4B. The cancer has spread to organs and tissues outside the abdomen, such as the liver, lungs, or groin lymph nodes.
Secondary peritoneal cancer
Secondary peritoneal cancer is staged according to the primary cancer site. When a primary cancer spreads to another part of the body, such as the peritoneum, it’s usually classified as a stage 4 of the original cancer.
A 2013 studyTrusted Source reported that almost 15 percent of people with colorectal cancer and almost 40 percent of people with stage 2 to 3 stomach cancer had peritoneal involvement.
Peritoneal cancer causes and risk factors
The cause of peritoneal cancer isn’t known.
For primary peritoneal cancer, risk factors include:
- Age. As you get older, your risk increases.
- Genetics. A family history of ovarian or peritoneal cancer increases your risk. Carrying the BRCA1 or BRCA2 gene mutation or one of the genes for Lynch syndrome also increases your risk.
- Hormone therapy. Taking hormone therapy after menopause slightly increases your risk.
- Weight and height. Being overweight or obese increases your risk. Those who are tall are at increased risk.
- Endometriosis. Endometriosis increases your risk.
Factors associated with decreased risk of peritoneal or ovarian cancer include:
- taking birth control pills
- bearing children
- tubal ligation, fallopian tube removal, or ovary removal
Note that ovary removal lessens the risk of peritoneal cancer but doesn’t completely remove it.
How peritoneal cancer is diagnosed
Diagnosis of both primary and secondary peritoneal cancer is difficult in the early stages. This is because the symptoms are vague and can easily be attributed to other causes.
Often peritoneal cancer is only found during surgery to remove a known tumor elsewhere in the abdomen.
Your doctor will physically examine you, take a medical history, and ask you about your symptoms. They may order a series of tests to determine a diagnosis.
Tests used to diagnose peritoneal cancer include:
- Imaging tests of the abdomen and pelvis. This may show ascites or growths. Tests include CT scan, ultrasound, and MRI. However, peritoneal cancer is difficult to imageTrusted Source using CT and MRI scans.
- Biopsy of an area that looks abnormal in a scan, including removal of fluid from ascites, to look for cancerous cells. Discuss the pros and cons of this with your doctor. The procedure also risks seeding the abdominal wall with cancerous cells.
- Blood tests to look for chemicals that may be elevated in peritoneal cancer, such as CA 125, a chemical made by tumor cells. A newer blood marker is HE4. It’s less likely than CA 125 to be elevated by noncancerous conditions.
- Laparoscopy or laparotomy. These are minimally invasive techniques to look directly at the peritoneum. They’re considered the “gold standard” in diagnosis.
Research into better and earlier methods of diagnosis for peritoneal cancer is ongoing.
A 2017 articleTrusted Source suggested the development of a “liquid biopsy.” This refers to a blood test that could look for a combination of tumor biomarkers. This would enable earlier treatment for some people.
How to tell the difference between peritoneal cancer and ovarian cancer in diagnosis
Peritoneal cancer is very similar to advanced epithelial ovarian cancer. Both involve the same type of cells. Criteria have been developed to distinguish them by the Gynecologic Oncology GroupTrusted Source.
It’s considered to be primary peritoneal cancer if the:
- ovaries appear normal
- cancerous cells aren’t on the ovary surface
- tumor type is predominantly serous (producing a fluid)
Two small studiesTrusted Source reported that the average age of people with primary peritoneal cancer was older than those with epithelial ovarian cancer.
Treating peritoneal cancer
You’re likely to have a treatment team including:
- a surgeon
- an oncologist
- a radiologist
- a pathologist
- a gastroenterologist
- a pain specialist
- specialized nurses
- palliative care specialists
Treatment for primary peritoneal cancer is similar to that for ovarian cancer. For both primary and secondary peritoneal cancer, individual treatment will depend on the location and size of the tumor and your general health.
Treatment for secondary peritoneal cancer also depends on the status of the primary cancer and your response to treatment for it.
Surgery is usually the first step. A surgeon will remove as much of the cancer as possible. They may also remove:
- your uterus (hysterectomy)
- your ovaries and fallopian tubes (oophorectomy)
- the layer of fatty tissue near the ovaries (omentum)
Your surgeon will also remove any abnormal-looking tissue in the abdominal area for further testing.
Advances in the precision of surgical techniques, known as cytoreductive surgery (CRS), have enabled surgeons to remove more of the cancerous tissue. This has improved the outlook of people with peritoneal cancer.
Your doctor may use chemotherapy before surgery to shrink the tumor in preparation for surgery. They may also use it after surgery to kill any remaining cancerous cells.
A newer method of delivering chemotherapy after surgery has increased its effectiveness in many cases.
The technique uses heat combined with chemotherapy delivered directly to the peritoneal cancer site. It’s known as hyperthermic intraperitoneal chemotherapy (HIPEC). This is a one-time treatment given directly after surgery.
The combination of CRS and HIPEC has “revolutionized” peritoneal cancer treatment, according to many researchers. But it isn’t fully accepted as standard treatment yet. This is because there aren’t randomized patient trials with control groups.
Research is ongoing. HIPEC is not recommended when there are metastases outside the abdomen and in some other situations.
All chemotherapy has side effects. Discuss what these might be and how to handle them with your treatment team.
In some cases, a targeted therapy drug may be used. These drugs are aimed at stopping cancer cells without harming normal cells. Targeted therapies include the following:
Monoclonal antibodies target substances on cells that promote cancer cell growth. These may be combined with a chemotherapy drug.
PARP (poly-ADP ribose polymerase) inhibitors block DNA repair.
Angiogenesis inhibitors prevent blood vessel growth in tumors.
Hormonal therapy, radiation therapy, and immunotherapy may also be used in some cases of primary peritoneal cancer.
What’s the outlook?
The outlook for people with primary or secondary peritoneal cancer has greatly improved in recent decades because of advances in treatment, but it’s still poor. This is mostly because peritoneal cancer usually isn’t diagnosed until it’s in an advanced stage. Also, the cancer may return after treatment.
Symptoms are hard to pinpoint, but if you have some of the general symptoms that persist, check in with your doctor. Earlier diagnosis leads to a better outcome.
Primary peritoneal cancer
As of 2019, the five-year survival rate for women with all types of ovarian, fallopian tube, and peritoneal cancers is 47 percent. This figure is higher for women under 65 (60 percent) and lower for women over 65 (29 percent).
Survival statistics for primary peritoneal cancer come from very small studies.
For example, a 2012 studyTrusted Source of 29 women with primary peritoneal cancer reported an average survival time of 48 months after treatment.
This is considerably better than the five-year survival rate reported in a 1990 study that ranged between 0.0 to 26.5 percentTrusted Source.
Secondary peritoneal cancer
Survival rates for secondary peritoneal cancer also depend on the stage of the primary cancer site and type of treatment. A small number of studies show that a combined treatment of CRS and HIPEC improves survival rates.
For example, a study reported in 2013 looked at 84 people with colorectal cancer that had spread to the peritoneum. It compared those who had systemic chemotherapy to those who had CRS and HIPEC.
Survival for the chemotherapy group was 23.9 months compared to 62.7 months for the group treated with CRS and HIPEC.
Seek out support
You may want to talk with other people going through treatment or with their family members.
The American Cancer Society support line is available 24/7 a day at 800-227-2345. They can help you find an online or local group for support.
Your treatment team may also be able to help with resources.