Peritoneal cancer is difficult to diagnose, especially because it often cannot be detected by radiological imaging. As a result, the incidence of peritoneal cancer has long been underestimated, and it was considered to be a very rare disease. Even today, the reported incidence rates of peritoneal cancer vary widely, but increasing awareness has led to increases in the reported incidence of peritoneal cancer in more recent studies. However, the “true” incidence is potentially higher because autopsy studies have found undetected peritoneal metastases in many cancer patients.
Malignant mesothelioma is a truly rare disease because it is diagnosed in approximately one to three patients per 1.000.000 persons per year. The disease is three times more common in men compared with women, and the risk of developing the disease increases with age. Malignant mesothelioma is mainly diagnosed in people who are 60 years and older, although younger patients have been described. The number of patients is expected to increase over the next few years due to individuals with past asbestos exposure.
Pseudomyxoma peritonei (PMP) is another rare subtype of peritoneal cancer. Studies on the incidence of PMP are hampered by difficulties in the definition and nomenclature for this disease. Most reports suggest the incidence of PMP is one to two patients per 1.000.000 persons per year, and the incidence of PMP is somewhat higher in women than in men.
In contrast to mesothelioma and PMP, peritoneal cancer arising from a malignant tumor elsewhere is in the body is much more common and affects hundreds of thousands of patients each year. This form of peritoneal cancer should be regarded as a metastatic disease from the primary tumor. Therefore, this form is often referred to as “peritoneal metastases”. Virtually every primary tumor in the human body can cause peritoneal cancer, but tumors from the gastrointestinal tract and the ovaries in women are, by far, the most common sources. It is thought that at least 10% of patients with colon cancer will develop peritoneal cancer during their disease. Patients with gastric cancer have an even higher incidence of peritoneal cancer, which is thought to be approximately 30% of patients. More detailed information on the incidence of specific subtypes may be found in the “Knowledge Base”.