All organs of the abdominal cavity - such as the stomach and intestine - and the abdominal wall are covered by a thin layer of cells. This layer is called "the peritoneal line" or "the peritoneum." Unfortunately, the peritoneum can be invaded by malignant cells. This condition is more commonly referred to as "peritoneal cancer", but it has also been called peritoneal surface malignancy ("PSM"), peritoneal carcinomatosis, peritoneal metastasis or peritoneal pseudomyxoma ("PMP").

Three differents possible origins

In peritoneal cancer, there are three different potential origins for malignant cells. First, cancer can originate from the so-called mesothelial cells that make up the peritoneum, which results in a very rare type of cancer called "malignant mesothelioma".
The second (and also rare) source of cancer cells is a mucus-producing tumor, which is more frequently located in the appendix. This tumor may rupture when it grows, and the rupture will spread mucus-producing cells to the abdomen. Eventually the abdomen fills with mucus, which leads to a condition known as peritoneal pseudomyxoma (PMP).

Finally - and being the most common - peritoneal cancer originates from cancer cells that are spread by a primary tumor at another site in the body. The cells travel to the peritoneum and begin to grow on the peritoneal surface. Almost any primary tumor in the body can cause this disease, but the abdominal organs, such as the colon, stomach and ovaries, are the most common organs of origin. Typically the malignant cells will multiply and form small tumor nodules (between 2 to 5mm) on the peritoneum. However, larger tumors are not rare, and sometimes bulky nodule conglomerates can develop in advanced stages. Peritoneal cancer nodules can occur anywhere in the abdominal cavity, but the most common sites include the right diaphragm, small pelvis, omentum and intestinal surface.

These cancerous nodules will eventually clog the intestinal handles and cause the accumulation of fluid in the abdomen (eg "malignant ascites"). Peritoneal cancer should be considered as a very serious and advanced form of cancer.