All of the organs in the abdominal cavity – such as the stomach and the intestine – and the abdominal wall are covered with a thin layer of cells. This layer is called ‘the peritoneal lining’ or ‘the peritoneum’. Unfortunately, the peritoneum can be invaded by cancer cells. This condition is most commonly referred to as “peritoneal cancer,” but it has also been called peritoneal surface malignancy (“PSM”), peritoneal carcinomatosis, peritoneal metastases or pseudomyxoma peritonei (“PMP”).
In peritoneal cancer, there are three different potential origins for the cancer cells. First of all, the cancer may arise from the so-called mesothelial cells that line the peritoneum, which results in a very rare type of cancer called “malignant mesothelioma”.
The second (and similarly rare) source of cancer cells is a mucus-producing tumor, which is most often situated in the appendix. This tumor may rupture when it grows, and the rupture spreads mucus-producing cells throughout the abdomen. Eventually, the abdomen is filled with mucus, which leads to a condition called pseudomyxoma peritoneior PMP.
Finally – and most commonly – peritoneal cancer arises from cancer cells that are shed by a primary tumor elsewhere in the body. The cells travel to the peritoneum and start to grow on the peritoneal surface. Almost any primary tumor in the body can cause this disease, but abdominal organs, such as colon, stomach and ovaries are the most common organs of origin. Typically, the cancer cells will go on to multiply and form small tumor nodules (between 2 to 5 mm) on the peritoneum. However, larger tumors are not uncommon, and sometimes, conglomerate masses of nodules may develop in advanced stages. The peritoneal cancer nodules may occur anywhere in the abdominal cavity, but the most common sites include the right diaphragm, the small pelvis, the omentum and the surface of the intestine.
Peritoneal cancer nodules and malignant ascites
These cancerous nodules will eventually obstruct the bowels and cause fluid to accumulate in the abdomen (i.e., “malignant ascites”). Peritoneal cancer should be regarded as a very serious and advanced form of cancer.