Pseudomyxoma peritonei is a rare and unusual cancer condition that develops slowly over years, often going unnoticed until the abdomen becomes filled with a jelly-like substance produced by cancer cells—earning it the nickname “jelly belly.” Understanding this complex condition can help patients and families navigate diagnosis and treatment with greater confidence.

Understanding the Disease

Pseudomyxoma peritonei, often abbreviated as PMP, is an extremely rare cancer that affects the peritoneal cavity, which is the space inside your abdomen and pelvis. The name literally means “false mucinous tumor of the peritoneum,” and it describes a condition where cancer cells spread throughout the abdominal area while producing large amounts of mucin—a thick, jelly-like substance that is one of the components of mucus.^[1]

What makes this disease unusual is how it behaves. Unlike typical cancers that form solid tumors and spread through the bloodstream or lymphatic system to distant parts of the body, PMP stays contained within the abdomen. The cancer begins as a growth, usually a polyp in the appendix, which eventually ruptures. When this happens, cancer cells that produce mucin escape into the peritoneal cavity and begin coating the surfaces of abdominal organs.^[3]

Healthcare providers sometimes call PMP a “borderline malignancy” because while it is indeed cancerous, it develops very slowly and doesn’t typically spread outside the abdomen the way most cancers do. Instead, the mucin-producing cells follow the natural flow of peritoneal fluid within the abdomen, settling in specific areas where they continue to produce more and more jelly-like material.^[2]

Epidemiology

Pseudomyxoma peritonei is remarkably rare. Research indicates that only about 1 to 4 people per million develop this condition each year, making it one of the more uncommon cancer diagnoses.^[1][2] To put this in perspective, you would need to examine the population of a medium-sized city to find just a handful of cases annually.

The disease tends to affect people later in life, with the average age at diagnosis being around 53 years. Women appear to be affected more frequently than men, though the appendix—not the ovaries—is the primary origin site in most cases. Initially, medical experts believed that ovarian tumors caused many PMP cases in women, but more recent understanding reveals that these ovarian findings are usually secondary spread from an appendiceal tumor that went unnoticed.^[2]

Because PMP develops so slowly and symptoms can take years to appear, many patients are diagnosed at an advanced stage when the disease has already spread throughout the peritoneal cavity. Some cases are discovered entirely by accident during medical procedures or imaging studies performed for unrelated health concerns.^[3]

Causes

The exact cause of pseudomyxoma peritonei remains unclear to medical experts. Scientists understand the sequence of events that leads to the condition, but they haven’t pinpointed why that sequence begins in the first place. What is known is that PMP almost always originates from mucinous tumors, with the appendix being the starting point in approximately 90 percent of cases.^[2]

The process begins when cells in the appendix develop abnormally and form a tumor that produces mucin. These cells continuously generate mucus inside the appendix, creating what doctors call a mucocele—essentially a mucus-filled sac. Over time, as more mucin accumulates, pressure builds until the appendix eventually ruptures.^[2]

When the appendix breaks open, the mucin-producing tumor cells spill into the peritoneal cavity. Because these cells lack normal adhesive properties that would keep them in one place, they float freely within the peritoneal fluid and spread throughout the abdomen. This movement follows predictable patterns based on how fluid naturally circulates in the abdominal cavity and the pull of gravity.^[2]

While appendiceal tumors are the most common source, PMP can occasionally originate from other organs including the colon, stomach, pancreas, gallbladder, or even the ovaries, though these cases are much rarer. Some research has identified genetic mutations, particularly in the KRAS gene, in a significant number of appendiceal tumors, but more research is needed to understand the complete genetic picture.^[5]

Risk Factors

Because pseudomyxoma peritonei is so rare and its underlying causes are not fully understood, identifying clear risk factors has proven challenging for researchers. However, some associations have been observed that may increase the likelihood of developing this condition.

One established risk factor is having familial adenomatous polyposis (FAP), a genetic condition that causes people to develop numerous polyps in their colon and rectum. People with FAP have a higher risk of developing mucinous adenocarcinoma of the appendix, which can lead to PMP.^[2]

Gender appears to play a role, with women being diagnosed more frequently than men. However, this statistical difference may be partly explained by historical misdiagnosis of appendiceal cancers as ovarian cancers in women. When the appendix ruptures, mucin can coat the ovaries, making it initially appear that the ovaries are the source of the problem.^[3]

Age is another consideration, as most people diagnosed with PMP are in their 50s or older. This reflects both the slow-growing nature of the disease and the time it takes for symptoms to become noticeable enough to prompt medical investigation.

Unlike many other cancers, PMP does not appear to be associated with lifestyle factors such as smoking, diet, alcohol consumption, or environmental exposures. This makes prevention particularly challenging, as there are no behavioral changes people can make to reduce their risk.

Symptoms

One of the most challenging aspects of pseudomyxoma peritonei is that symptoms develop very gradually and can be easily mistaken for common, minor digestive problems. Many people live with PMP for years before realizing something serious is wrong. The slow accumulation of mucin in the abdomen means that early symptoms are often vague and intermittent.

The most common symptom is abdominal distension, which is a noticeable swelling or enlargement of the belly. This happens as mucin accumulates and takes up more space in the abdominal cavity. Some people notice their clothes fitting more tightly around the waist or find they need larger sizes despite not gaining weight elsewhere on their body. This progressive swelling is what gives PMP its colloquial name “jelly belly.”^[1]

Abdominal pain or discomfort is another frequent complaint. This may feel like a general sense of fullness, pressure, or aching in the belly. The pain typically isn’t severe initially, which is why many people dismiss it or assume it’s related to overeating, gas, or indigestion.^[1]

Changes in bowel habits commonly occur as the growing volume of mucin begins to press on the intestines. Constipation is particularly common because the pressure can partially block the large intestine, making it difficult to pass stool normally. Some people experience a feeling of incomplete bowel movements or need to strain more than usual.^[1]

In men, hernias—particularly inguinal hernias in the groin area—can be an early sign of PMP. The increased pressure in the abdomen from mucin buildup can push organs or tissue through weak spots in the abdominal wall. Women may experience difficulty conceiving, as mucin accumulation or inflammation can affect the reproductive organs.^[1]

Loss of appetite and nausea may develop as the condition progresses. The physical presence of mucin in the abdomen can create a sensation of fullness even when little food has been eaten. Unlike many cancers, however, PMP patients often do not experience dramatic weight loss or cachexia (severe wasting) until very late stages of the disease.^[3]

Because these symptoms are non-specific and develop slowly, diagnosis is often delayed. Some patients only learn they have PMP during surgery for what was thought to be appendicitis, a hernia, or an ovarian cyst.

Prevention

Unfortunately, there are no known methods to prevent pseudomyxoma peritonei. Because the exact causes of the disease remain unclear and it doesn’t appear to be linked to lifestyle factors, diet, or environmental exposures, there are no specific preventive measures individuals can take to reduce their risk of developing this condition.

The lack of identifiable risk factors in most cases means that routine screening programs, similar to those used for breast or colon cancer, are not feasible for PMP. The extreme rarity of the disease also makes widespread screening impractical from both a cost and resource perspective.

For individuals with familial adenomatous polyposis (FAP), regular monitoring of the colon and appendix as part of their overall cancer surveillance program may help detect appendiceal abnormalities earlier. However, even in these high-risk individuals, PMP remains uncommon.^[2]

What is important is awareness of unusual or persistent abdominal symptoms. While PMP cannot be prevented, earlier detection can potentially improve treatment outcomes. Anyone experiencing progressive abdominal swelling, persistent changes in bowel habits, unexplained abdominal discomfort that doesn’t resolve, or other concerning digestive symptoms should seek medical evaluation rather than assuming these issues are minor or will resolve on their own.

Pathophysiology

Understanding how pseudomyxoma peritonei develops and spreads requires looking at the unique way this disease behaves within the body. The pathophysiology of PMP involves several distinct stages that unfold over months to years.

The process begins in the appendix, where cells lining the organ undergo changes that cause them to produce excessive amounts of mucin. These cells form a low-grade mucinous tumor, most commonly called a Low-Grade Appendiceal Mucinous Neoplasm (LAMN). As the tumor grows and produces more mucin, the appendix becomes distended, creating a mucocele.^[3]

Eventually, the pressure from accumulated mucin causes the appendix to rupture. This rupture releases tumor cells into the peritoneal cavity—the space between the abdominal wall and the organs. These free-floating mucinous epithelial cells are unique because they lack the normal adhesive molecules that would cause them to stick in one place. Instead, they flow freely with peritoneal fluid throughout the abdominal cavity.^[2]

The distribution of tumor cells within the abdomen follows predictable patterns, a phenomenon called the “redistribution phenomenon.” Peritoneal fluid circulates naturally in the abdomen, moving upward along the right side toward the diaphragm (the muscle that separates the chest from the abdomen) and flowing around and through various spaces between organs. Tumor cells travel with this fluid and eventually get trapped in areas where fluid is reabsorbed through tiny lymphatic channels.^[2]

The most common sites where mucin and tumor cells accumulate include the right upper abdomen near the liver and diaphragm, the omentum (a fatty apron-like structure that covers the intestines), the pelvis (where gravity causes fluid to pool), and along the surfaces of the colon and small intestine. These cells continue producing mucin wherever they settle, leading to progressive accumulation of the jelly-like material.

Unlike aggressive cancers that invade deep into tissues and organs, PMP typically remains on the surface of organs, coating them with mucin rather than infiltrating into them. This surface-level spread is one reason why the disease can sometimes be surgically removed more completely than other types of peritoneal cancers.

Over time, the accumulating mucin causes several problems. It creates physical pressure on organs, particularly the intestines, leading to compression and dysfunction. The mucin can prevent normal organ movement and function, causing bowel obstruction, impaired digestion, and eventually organ failure if left untreated. The inflammatory response to the mucin also causes the peritoneum to thicken and become scarred, a process called fibrosis, which further impedes normal organ function.^[5]

The disease is classified based on the cellular characteristics of the tumor. Low-grade tumors contain cells that look relatively normal under the microscope and grow slowly, while high-grade tumors have more abnormal-appearing cells and tend to be more aggressive. The presence of signet ring cells—cells filled with mucin that push the nucleus to one side, giving them a distinctive appearance—generally indicates a more aggressive form of the disease.^[5]