Pseudomyxoma Peritonei: Definition

Print this article

Pseudomyxoma peritonei, usually shortened to PMP, is the name for jelly-like mucin collecting inside the abdominal cavity. The name comes from Greek and Latin roots meaning false mucous tumor of the peritoneum.

PMP describes where material has ended up rather than naming a tumor type. It is a clinical and pathologic picture, and the report will usually also name the tumor it came from.

Most cases begin with a low-grade appendiceal mucinous neoplasm. The appendix fills with mucin, its wall thins and eventually gives way, and mucin escapes into the abdomen. Less often, PMP arises from mucinous tumors of the ovary, colon, or pancreas.

How does pseudomyxoma peritonei behave?

PMP behaves differently from most cancers, and understanding that difference explains much of how it is managed.

Mucin accumulates slowly, over years rather than weeks. It gathers where fluid naturally pools, under the diaphragm, in the pelvis, and across the omentum. Rather than destroying organs, it presses on them and coats their surfaces.

PMP also rarely travels through the bloodstream to distant organs such as the liver or lungs, which is the usual route for other cancers. It stays within the abdominal cavity. The problems it causes come from accumulation and pressure, leading to swelling, discomfort, hernias, and eventually blockage of the bowel.

How is pseudomyxoma peritonei diagnosed?

PMP is usually suspected first on a scan that shows mucin distributed through the abdomen, and confirmed when a pathologist examines tissue or fluid.

The pathologist answers two questions. The first is whether the mucin contains tumor cells. The second is what those cells look like, if any are present. The answers determine the grade, and the grade matters far more than the amount of mucin.

Acellular mucin. Mucin with no tumor cells found in it. This carries the best outlook, because the material cannot grow on its own.
Low-grade mucinous carcinoma peritonei. Mucin-containing cells that look only mildly abnormal. Older reports may call this disseminated peritoneal adenomucinosis, or DPAM.
High-grade mucinous carcinoma peritonei. Mucin-containing clearly abnormal cells. Older reports may call this peritoneal mucinous carcinomatosis, or PMCA. This behaves more like a conventional cancer.

A further category is used when signet ring cells are present, which again carries a less favorable outlook.

How is pseudomyxoma peritonei treated?

Treatment is concentrated in a small number of specialized centers, because both the surgery and the judgment involved are highly specific to this disease.

The main approach combines two things. Cytoreductive surgery is a long operation to remove all visible disease from the abdomen, often including the omentum and parts of other organs. Heated chemotherapy is then delivered directly into the abdominal cavity during the same operation, a technique known as HIPEC.

Whether this approach is suitable depends on the grade of the disease, how widely it is distributed, whether all visible disease can be removed, and your general health. Some people with limited or acellular disease are followed with imaging instead, and treated only if the disease progresses.

What is the outlook?

The outlook varies widely and depends mostly on grade.

People with acellular mucin do very well, with reported five-year survival around 90% or higher. Low-grade disease carries reported five-year survival of roughly 70 to 80% after treatment at a specialist center. High-grade disease is reported at around 55%.

These figures come from groups of patients treated over many years and cannot predict any individual outcome. Recurrence is common even after successful surgery, and repeat operations are sometimes possible. Many people live with PMP for a long time, and it is often managed more like a chronic condition than a single episode of treatment.

Questions to ask your doctor

What type of tumor caused my pseudomyxoma peritonei?
Did the mucin found in my abdomen contain tumor cells?
What grade was assigned, and what does that grade mean?
How widely distributed is the disease in my abdomen?
Am I a candidate for cytoreductive surgery and HIPEC?
Should I be referred to a center that specializes in this disease?
If surgery is not appropriate now, what would change that?
How will I be monitored, and how often?
What symptoms should prompt me to call between appointments?