Primary peritoneal cancer

Primary peritoneal cancer (PPC) is a rare cancer. It starts in the thin layer of tissue lining the inside of the abdomen. This tissue lining is called the peritoneum. 

PPC cells are the same as the most common type of ovarian cancer cells.  This is because the lining of the abdomen and the surface of the ovary come from the same tissue when we develop from embryos in the womb. So doctors treat PPC in the same way as ovarian cancer.

What is the peritoneum?

The peritoneum covers all of the organs within the tummy (abdomen), such as the bowel and the liver. It protects the organs and acts as a barrier to infection. It has 2 layers. One layer lines the abdominal wall and is called the parietal layer. The other layer covers the organs and is called the visceral layer.

There is a small amount of fluid between the two layers, which separates them and allows them to slide over each other. This fluid allows us to move around without causing any friction on the layers.

About primary peritoneal cancer

PPC mainly affects women. It's very rare in men. Most people are over the age of 60 when they are diagnosed.

There are no exact numbers for how many people get it in the UK. American research suggests that around 10 out of 100 (around 10%) of all women with ovarian, fallopian and peritoneal serous cancers have PPC. 

The causes of PPC are unknown. Most cancers are caused by a number of different factors working together. Research suggests that a very small number of PPCs may be linked to the inherited faulty genes BRCA 1 and BRCA 2. These are the same genes that increase the risk of ovarian cancer and breast cancer. 

Symptoms

Symptoms for primary peritoneal cancer can be very unclear and difficult to spot. Many of the symptoms are more likely to be caused by other medical conditions.

The symptoms of PPC include:

• a swollen tummy (abdomen)
• abdominal pain
• constipation or diarrhoea
• feeling or being sick
• feeling bloated
• loss of appetite

Tests to diagnose

You might have the following tests to diagnose primary peritoneal cancer.

Pelvic examination

Most people start by seeing their GP. They might want to examine your abdomen. They will press gently on the outside of your abdomen to feel for any lumps, or tender areas.

Your doctor might also want to examine you internally. This is to see if your abdomen, including your womb and ovaries, feels normal. Your doctor will ask you to lie on your back on the couch with your feet drawn up and your knees apart.

They will then put one or two gloved fingers into your vagina. At the same time they press down on your abdomen with the other hand. If any part of the abdomen is enlarged, or if a lump of any kind is there, your doctor might be able to feel it.

Blood tests

Primary peritoneal cancers often produce a protein called CA125 that shows up in a blood test. Doctors call this a tumour marker.

A raised level of CA125 can be a sign of either PPC, ovarian cancer or fallopian tube cancer. But it can be raised for other reasons, such as:

• endometriosis

• fibroids

• pregnancy

• pelvic inflammatory disease

Scans

You might need to have an ultrasound scan to help make a diagnosis. An ultrasound uses sound waves to build up a picture of a part of the body. You might have an abdominal ultrasound or a transvaginal ultrasound.

Your doctor may also want you to have a CT scan or MRI scan to check whether the cancer has spread within your abdomen. 

Stages

The stage of a cancer shows how big it is and whether it has spread. This helps doctors to decide which treatment people need.

The staging system for PPC is the same as for ovarian cancer, but there is no early stage. PPC is always either stage 3 or stage 4. This is an advanced cancer.

Treatment

The treatment you have depends on a number of things including:

• the size of your cancer

• where the cancer is in the abdomen, and if it has spread further away

• your general health

The treatment for PPC is the same as for advanced epithelial ovarian cancer. 

The aim of treatment for advanced cancer is usually to shrink the cancer and control it for as long as possible. You might have the following treatments.

Surgery

The aim of surgery is to remove as much of the cancer from the abdomen as possible before chemotherapy. This is called debulking surgery.

Chemotherapy tends to work better when there are only small tumours inside the abdomen. The surgery usually includes removing your womb, ovaries, fallopian tubes and the layer of fatty tissue called the omentum.

The surgeon will also remove any other cancer that they can see at the time of surgery. This could include part of the bowel if the cancer has spread there.

Sometimes PPC can grow so that it blocks the bowel or the urinary system. You might need surgery to unblock these if this happens.

Chemotherapy

Chemotherapy uses anti cancer (cytotoxic) drugs to destroy cancer cells. These drugs work by disrupting the growth of cancer cells. The drugs circulate in the bloodstream around the body.

You may have chemotherapy:

• before surgery to reduce the size of the cancer

• after surgery when you have recovered

• on its own if you are unable to have surgery

The most common chemotherapy drugs used to treat PPC are a combination of carboplatin and paclitaxel (Taxol).

Radiotherapy

Radiotherapy uses high energy x-rays to kill cancer cells. Radiotherapy isn't often used for PPCs. But doctors may use it to shrink tumours and reduce symptoms.

Other treatments

You can have treatment to control symptoms, such as pain and fluid in the abdomen (ascites), even if you are unable to have chemotherapy.

Fluid can build up between the two layers of the peritoneum. It can be very uncomfortable and heavy.

Your doctor can drain the fluid off using a procedure called abdominal paracentesis or an ascitic tap. The diagram below shows this.

Research

Researchers around the world are looking at better ways to diagnose and treat ovarian cancer. Some trials for advanced ovarian cancer are also open for people with PPC

Go to Cancer Research UK’s clinical trials database to read about trials for ovarian cancer in the UK. The trial summary includes information about who can take part in the trial. You need to talk to your specialist if there are any trials that you think you might be able to take part in.

Coping

Coping with cancer, particularly when it's rare can be difficult, both practically and emotionally. Your doctor and cancer specialist nurse will help support you.

Being well informed about your condition and its treatment can help you to make decisions and cope with what happens.