Pseudomyxoma peritonei (PMP): symptoms, diagnosis and treatment

Macmillan Cancer Support describes PMP as a rare cancer that usually starts in the appendix, though it can start in another part of the bowel, the bladder or the ovaries. The tumour usually grows slowly. Unlike most cancers, PMP rarely spreads through the bloodstream or lymphatic system. Instead PMP cells attach to the peritoneum, the layer of tissue that lines the inside of the abdomen, and make a jelly-like substance called mucin that collects there.

Cancer Research UK says that, without treatment, it will take over the peritoneal cavity and can press on the bowel and other organs. Because it develops very slowly, it has usually spread beyond the appendix by the time it is diagnosed. It also describes PMP as a borderline malignant condition: it does not behave like most cancers, but it does grow and spread inside the abdomen.

Macmillan says PMP may not cause any symptoms in its early stage. Cancer Research UK says some people will not have symptoms, which is one reason it can be difficult to diagnose. Symptoms can include:

• a gradual increase in waist size, swelling and bloating of the abdomen

• pain in the abdomen or pelvis

• a hernia (a bulge in the tummy wall or groin)

• loss of appetite or a feeling of fullness

• unexplained weight gain (Macmillan)

• a change in bowel habit, for example diarrhoea, constipation or leaking

• not being able to become pregnant (Cancer Research UK)

Doctors do not know what causes PMP, according to both Macmillan and Cancer Research UK. Cancer Research UK says it usually begins as a small growth in the appendix called a low grade appendiceal mucinous neoplasm (LAMN), which is different from the polyps that cause bowel cancer, and that it can start elsewhere, for example in the bowel or ovary, but this is even rarer. It is more common in women than in men.

It is a rare cancer. Cancer Research UK explains that in the UK and Europe, experts say a cancer is rare if fewer than 6 in 100,000 people are diagnosed each year.

Macmillan says PMP is rare and can be difficult to diagnose, since symptoms can be caused by many other conditions. It may be found during abdominal surgery for another reason. Cancer Research UK says doctors can sometimes only diagnose it properly after an operation to look into the abdomen, and that in women it can sometimes be confused with ovarian cancer, which may also cause a swollen abdomen and in some types produce mucin.

• CT scan, ultrasound scan and MRI scan to look at the abdomen.

• Drainage of fluid from the abdomen (peritoneal aspiration) so a sample can be tested.

• A CT- or ultrasound-guided biopsy, where a needle takes a small piece of tissue for examination under a microscope.

• A biopsy taken during keyhole surgery (laparoscopy), or an operation to look into the abdomen (laparotomy).

Both charities say the main treatments are surgery and chemotherapy. A team of specialists, called a multidisciplinary team, discusses the best treatment for you. Cancer Research UK says your treatment depends on where the cancer is and your general health.

Cancer Research UK says the surgeon strips out the lining of the abdomen and removes any tissue affected by PMP. Depending on the person this can include part of the bowel, the spleen, the omentum (a fatty layer in the abdomen), the gallbladder, part of the rectum, the womb and ovaries, and the bellybutton. Heated chemotherapy is then put into the abdomen, usually mitomycin C, and left for 60 to 90 minutes according to Macmillan before being drained.

This is major surgery. Cancer Research UK says the operation can take around 10 hours and recovery can be slow, and sometimes people need more than one operation. After surgery you are likely to spend 24 to 48 hours in intensive care or a high dependency unit and 2 to 3 weeks in hospital in total. It can be at least 6 months before you are fully active again and able to work.

Cancer Research UK says about 30 out of every 100 people (30%) have complications after this treatment, which might be less in some treatment centres, and about 20 out of 100 (20%) need a stoma, around half of whom only need it for 3 to 6 months. If the spleen is removed you may need vaccinations and lifelong antibiotics.

Because PMP is rare, NICE recommends that people with PMP have cytoreductive surgery with intraperitoneal chemotherapy in a specialist centre. Cancer Research UK and Macmillan say there are two designated specialist treatment centres in the UK, so you may need to travel and stay in hospital longer. Chemotherapy into a vein can usually be given at your local cancer centre.

Macmillan says you will have regular check-ups during and after treatment and should tell your doctor or specialist nurse as soon as possible about new symptoms between appointments. Surgery and treatment can affect fertility, sex life and body image, and Macmillan advises asking your consultant or clinical nurse specialist about fertility before treatment, because if the womb and ovaries are removed you will not be able to get pregnant. Recovery takes time, and support is available through your GP or cancer team.

See a GP if you have a growing waist or persistent bloating, abdominal or pelvic pain, a new hernia or a change in bowel habit that does not settle. If you have been treated for PMP, tell your specialist team quickly about new symptoms.

On the NHS, the GP refers you for scans, and if PMP is suspected you are referred to a specialist centre where a multidisciplinary team plans treatment. Cancer Research UK notes that NICE guidance supports treatment in designated specialist centres. Some people seek a second opinion privately, and it is reasonable to ask any provider how often their team performs this operation.