Peritoneal Cancer: A Rare Abdominal Cancer

Peritoneal cancer, also called primary peritoneal cancer, is a rare type of cancer, occurring in fewer than seven out of every million people in the United States.

The peritoneum is a membrane that lines the abdominal cavity. It houses the digestive tract, liver, and other organs. Peritoneal cancer can first begin in the abdominal cavity (known as primary peritoneal cancer) or spread to the peritoneum from cancer that started elsewhere.

Symptoms of peritoneal cancer are often vague, making it difficult to diagnose until the cancer is advanced. It is often fatal, though new treatments for peritoneal cancer are improving survival rates.

This article details the anatomy of the peritoneum and how peritoneal cancer is diagnosed and treated.

The Peritoneum Lines the Abdominal Cavity

The peritoneum is a two-layered membrane composed of epithelial cells. It lines the abdominal and pelvic cavity organs, covering the digestive tract, liver, and reproductive organs.

The peritoneal membranes and the fluid between the membranes protect the organs, allowing them to move freely against each other without sticking or rubbing.

Peritoneal cancer may develop anywhere within the abdominal or pelvic cavity and, when it spreads, it often spreads to the surface of abdominal and pelvic organs.

Symptoms of Peritoneal Cancer

People with peritoneal cancer often have few symptoms until the disease is fairly advanced.

Other symptoms may include constipation, bowel changes, abnormal vaginal bleeding, an abdominal mass, or unintentional weight loss.

As the disease progresses, complications can include:

• Ascites (fluid build-up in the abdomen), causing abdominal discomfort, nausea and vomiting, and shortness of breath due to the pressure of the abdomen pushing upwards on the lungs
• Bowel obstruction, which may require the creation of a stoma, an opening from the intestine to the outside of the body to eliminate waste
• Urinary tract obstruction, which may require a stent to drain urine from the bladder or a nephrostomy tube to drain urine from the kidney

Causes and Risk Factors for Peritoneal Cancer

It’s not known precisely what causes peritoneal cancer, though the process begins when a series of mutations in peritoneal cells results in out-of-control growth.

Peritoneal cancer is much more common in females than males and has risk factors similar to the risk factors for ovarian cancer.

Risk factors include:

• Age, with most people who are diagnosed being over the age of 60
• A history of breast cancer
• The use of hormone replacement therapy (both combination and estrogen-only types)
• A history of endometriosis
• Obesity

Using talc below the waist is also linked with an increased risk.

In contrast, some factors are associated with a decreased risk of developing the disease. These include using oral contraceptives (the reduced risk may last 30 years after they are discontinued), having a tubal ligation, giving birth (especially before age 35), and breastfeeding.

Some people have preventive surgery to remove their fallopian tubes and ovaries (hysterectomy and salpingo-oophorectomy) due to a family history of ovarian cancer or a BRCA gene mutation. While this can reduce the risk of epithelial ovarian cancer by up to 90%, the risk of peritoneal cancer remains.

Genetics

A family history of ovarian, fallopian tube, or peritoneal cancer increases the risk of peritoneal cancer, and around 10% of these cancers are considered to be hereditary. Having certain genetic syndromes such as Lynch syndrome (hereditary non-polyposis colon cancer) or having a BRCA gene mutation increases the risk.

Women who carry a BRCA gene mutation have roughly a 5% risk of developing peritoneal cancer, even if their ovaries have been removed preventively.

Primary Peritoneal Cancer vs. Ovarian Cancer

Up to 15% of advanced serous ovarian cancer patients could have primary peritoneal cancer.

There are many similarities between primary peritoneal cancer and epithelial ovarian cancer, including similar symptoms, microscopic appearance, and each condition’s response to similar treatment methods.

The similarity between these two types of cancer helps plan treatment, as more research has been done on epithelial ovarian cancer because it’s much more common. Epithelial ovarian cancer occurs in roughly 120 out of 1 million people.

While peritoneal and ovarian cancers are similar, there are also significant differences. For example, people diagnosed with peritoneal cancer tend to be older than those with ovarian cancer.

The peritoneum and the surface of the ovarian stem form from the same tissue in fetal development. There is some thought that the peritoneal cells that give rise to peritoneal cancer may be leftover ovarian cells that remained in the abdomen during development.

The chance that debulking surgery will be successful is greater in peritoneal cancer than in ovarian cancer, but the overall survival rate is worse for peritoneal cancer.

Diagnosing Peritoneal Cancer

No screening test has been found effective in the early detection of primary peritoneal cancer, even for those with an elevated risk of developing the disease.

After listening to symptoms and performing a physical exam, there are several tests doctors may order when considering the diagnosis.

Blood Tests

The blood test CA-125 checks the level of a tumor marker that may be elevated in people with peritoneal cancer. That said, levels of CA-125 may be elevated in many conditions, from pelvic infections to pregnancy, and levels may be normal even in the presence of cancer.

Imaging Tests

Imaging studies can help evaluate the symptoms of peritoneal cancer. An ultrasound (transvaginal ultrasound) is often the first test performed. A computerized tomography (CT) scan or magnetic resonance imaging (MRI) scan of the abdomen and pelvis may also be helpful.

In addition, an upper and or lower GI series may be ordered.

Biopsy and Laparoscopy

Most often, a biopsy is needed for a definitive diagnosis. When ascites are present, paracentesis may be done. A needle is inserted through the skin into the abdominal cavity to drain fluid. This fluid can be examined under a microscope to look for the presence of cancer cells.

A biopsy is often taken during a laparoscopy, a minimally invasive procedure in which several small incisions are made in the abdomen, and instruments are inserted to remove tissue samples from the abdomen or pelvis.

Differential Diagnosis

Several conditions can mimic primary peritoneal cancer. Some of these include the different types of ovarian cancer, abdominal abscesses, cystic collection of fluid, bile, or lymph fluid, and metastases to the peritoneum from other types of cancer.

Staging

Unlike many cancers that are classified into stages from 1 to 4, primary peritoneal cancer does not have an early stage.

This disease is always defined as stage 3 or stage 4 at diagnosis.

• In stage 3 disease, cancer may have metastasized (spread) to the peritoneum outside of the pelvis or to lymph nodes near the back of the abdomen (retroperitoneal lymph nodes) but not to other organs outside the pelvis.
• With stage 4 peritoneal cancer, the tumor has usually metastasized to organs in the abdomen, such as the liver, or other body regions, such as the lungs.

Peritoneal Cancer Treatment Options

The treatment for peritoneal cancer will depend on a number of factors, including the location of the cancer, the stage, and a person’s general health.

Surgery

The surgery most often performed is cytoreduction or debulking surgery. The goal is to remove an optimal amount of cancer, but it’s often impossible to remove all of the cancer. The peritoneum itself cannot be removed.

After optimal cytoreductive surgery, there are not any areas of cancer left in the abdomen that are larger than 1 centimeter (about half an inch) in diameter. By reducing the amount of tumor present, survival improves, and chemotherapy can be more effective, as it works better if there are only small tumors in the abdomen.

During cytoreduction surgery, the surgeon removes all visible tumors. If the tumor cannot be separated from an organ, it may be partially or completely removed. This may include the gallbladder, spleen, part of the small or large intestine, the uterus, fallopian tubes, ovaries, and the primary location of cancer in the peritoneum. Sometimes the omentum, the fatty layer of tissue surrounding the intestines, is also removed (omentectomy).

Depending on the size and extent of cancer, nearby lymph nodes, as well as the appendix may be removed. Peritoneal cancer can spread extensively through the abdomen, and many areas of the tumor may need to be removed.

Chemotherapy

Chemotherapy is commonly used for treating peritoneal cancer. It can be started during or after surgery, or used alone for tumors that are widespread. Chemotherapy can be given intravenously or injected directly into the abdominal cavity (intraperitoneal chemotherapy).

Hyperthermic intraperitoneal chemotherapy is a fairly unique treatment that has proven beneficial for peritoneal cancer.

During this procedure, chemotherapy drugs are heated to 107.6 degrees F prior to being injected into the abdomen. Heat can kill cancer cells and may make chemotherapy more effective. It is most often used shortly after cytoreductive surgery has been completed for advanced peritoneal cancer.

Immunotherapy may be used in some cases.

Targeted Therapies

Targeted drugs are medications that target specific pathways involved in the growth of a specific type of cancer cell. Avastin (bevacizumab) is approved for use along with chemotherapy (followed by Avastin alone).

A class of drugs called PARP inhibitors, which inhibit the poly ADP ribose polymerase enzyme, may be used for women who carry BRCA gene mutations. The PARP inhibitors Lynparza (olaparib), Rubraca (rucaparib), and Zejula (niraparib) are approved for treating this type of cancer.

Radiation

Radiation is used infrequently for peritoneal cancer but may sometimes be useful for treating isolated areas of cancer.

Supportive/Palliative Care

Most people are diagnosed with peritoneal cancer only after it is in the advanced stages, when a cure is not possible. Yet, there are many things that can be done to improve quality of life.

• Paracentesis may improve breathing by draining fluid.
• Nutritional consultation may help with the loss of appetite associated with cancer, and reduce the risk of cancer cachexia (unintentional weight loss and muscle wasting).
• Management of nausea can improve quality of life.
• Pain management is important and controlling pain is an essential part of treatment.

Prognosis

While the prognosis of peritoneal cancer is generally poor, there have been documented cases of complete remission from the disease.

There are few studies looking at survival rates, and factors associated with better survival rates include the absence of cancer in the lymph nodes and complete cytoreduction surgery.

Coping

Coping with cancer is challenging, and the fact that many people have never heard of peritoneal cancer can add to the stress and anxiety of having this diagnosis. This can feel very isolating, especially when you see the communal support offered to people with other types of cancer.

While you are unlikely to find a support group for peritoneal cancer in your community due to the relative rarity of the disease, it is possible to connect with peritoneal cancer communities online.

In addition to these resources, some of the cancer organizations that represent ovarian cancer, as well as organizations that support people with many forms of cancer, may also be a source of support. Some, like CancerCare, even provide support groups and communities for friends and family members of people living with cancer as well.

Summary

Peritoneal cancer is a rare cancer that forms in the lining of the abdominal cavity, known as the peritoneum. Symptoms of peritoneal cancer are often vague and include fatigue, abdominal pain and swelling, urinary frequency, and a sense of fullness when eating. 

A diagnosis of peritoneal cancer is made through bloodwork, imaging studies, and a biopsy. It is treated by surgically removing as much of the cancer as possible, followed by chemotherapy, radiation, or other targeted therapies.