What it is, what causes it, and how it is treated.
Pseudomyxoma peritonei, usually shortened to PMP, is a rare condition in which jelly-like mucus builds up inside the abdomen. It is not a type of cancer on its own. It is caused by a mucin-producing tumor, most often one that starts in the appendix. People sometimes call it “jelly belly” because of the way the mucus collects and spreads.
What Causes PMP
PMP almost always starts with a mucinous tumor of the appendix, often a low-grade appendiceal mucinous neoplasm (LAMN). When that tumor breaks open, mucus and tumor cells escape into the abdominal cavity. The cells keep making mucin, which slowly collects on the surfaces of organs and the lining of the abdomen. Less often, PMP can come from a mucinous tumor in another organ, such as the ovary or bowel. The grade of the original tumor, low-grade or high-grade, shapes how the condition behaves and how it is treated.
Symptoms of PMP
PMP often grows slowly, and many people have no symptoms early on. It is sometimes found by chance during surgery or a scan done for another reason. When symptoms do appear, the most common ones are:
- A gradual increase in belly size or a feeling of pressure
- Bloating and lasting abdominal discomfort
- A new hernia, sometimes the first sign
- Loss of appetite or feeling full quickly
- Changes in bowel habits
- In women, what looks like an ovarian mass
How PMP Is Diagnosed
PMP is usually seen on a CT scan or MRI, which can show mucus collecting in the abdomen and pelvis. Many cases are confirmed during surgery, when the surgeon can see the mucinous material directly. A pathologist then examines the tissue to identify the tumor behind it and assign a grade. That grade matters, because it guides the treatment plan.
How PMP Is Treated
The main treatment for PMP is cytoreductive surgery combined with HIPEC. Cytoreductive surgery, or CRS, removes all the visible mucus and tumor from the abdomen. HIPEC is heated chemotherapy washed through the abdominal cavity at the end of that surgery to target cells too small to see. This is a major operation, and outcomes are meaningfully better when it is done at a specialty center with a team experienced in peritoneal surface malignancies. For very slow-growing, low-volume disease, a specialist may recommend careful monitoring instead of immediate surgery. These recommendations follow the 2025 Godfrey consensus guidelines for appendiceal tumors.
Because PMP is rare and CRS/HIPEC is complex, getting to an experienced peritoneal surface malignancy center is one of the most important decisions you can make. Find a specialist center here.
Frequently Asked Questions About Pseudomyxoma Peritonei
What is pseudomyxoma peritonei?
Pseudomyxoma peritonei, or PMP, is a rare condition where jelly-like mucus builds up in the abdomen. It is caused by a mucin-producing tumor, most often one that begins in the appendix. It is a condition, not a cell type of cancer by itself.
Is PMP a cancer?
PMP is caused by a tumor, and the tumor cells keep growing and spreading mucin, so it is treated as a serious condition that needs expert care. On its own, though, the term PMP describes the mucus buildup and its spread, not a specific type of cancer. The tumor behind it, and its grade, is what defines the diagnosis.
What causes pseudomyxoma peritonei?
It most often starts from a mucinous tumor of the appendix, frequently a low-grade appendiceal mucinous neoplasm that breaks open and releases mucus and cells into the abdomen. Less commonly, it comes from a mucinous tumor in another organ.
What are the first signs of PMP?
Many people have no early signs. When symptoms show up, a slowly growing belly, ongoing bloating, or a new hernia are among the most common. Because these are easy to mistake for other things, PMP is often found later or by accident.
How is PMP treated?
The standard treatment is cytoreductive surgery with HIPEC at an experienced specialty center. Surgery removes the visible mucus and tumor, and HIPEC delivers heated chemotherapy inside the abdomen to reach what surgery cannot. Some slow-growing cases are watched closely instead. Your specialist team decides based on your case.
Is PMP the same as appendix cancer?
They are closely linked but not the same. PMP is the mucus buildup in the abdomen. Appendix cancer is the tumor that often causes it. You can learn more about the tumor types on our types of appendix cancer page.
Sources: This page reflects the 2025 Godfrey consensus guidelines for appendiceal cancers, developed by the Peritoneal Surface Malignancies Consortium.
Medically reviewed by Dr. John Paul Shen, MD Anderson. Last reviewed July 2026.
If you or someone you love has appendix cancer or PMP, adding your data to the Patient-Led Global Appendix Cancer Registry helps drive research on this rare disease. United States: register here. International: register here.