Peritoneal cancer refers to cancer that develops within or more commonly, has spread to the peritoneum from other organs within the abdomen (known as peritoneal metastases). The peritoneum is the tissue that lines and protects the organs in the abdomen such as the stomach, bowel and ovaries.

The peritoneum is made of epithelial cells, which is the same type of tissue that lines the ovaries. This means that peritoneal cancer often acts and looks like ovarian cancer, from causing similar symptoms to requiring the same types of treatments.

Whilst primary tumours of the peritoneum are very rare, with women more likely than men to develop cancer in the peritoneum, spread to the peritoneum from other abdominal cancers, such as stomach, colon and ovarian cancers, is very common.

Primary peritoneal cancer can be described in stages depending on how early or advanced the cancer is. Primary peritoneal cancer is often diagnosed at a more advanced stage – Stage III or Stage IV, because the symptoms in the early stages are often missed.

Primary peritoneal cancer is staged using the same guidelines as ovarian cancer, known as the FIGO (International Federation of Gynaecology and Obstetrics) system. These stages give an indication of how little to how much the cancer has progressed.

As the staging of primary peritoneal cancer can be complex, it is important to discuss your individual diagnosis and stage with your specialist.

• Stage IIIA – the cancer has spread to the lymph nodes outside of the peritoneum, or to the surface of the peritoneum outside of the pelvis
• Stage IIIB – the cancer has grown into the peritoneum outside the pelvis and the cancer in the peritoneum is 2 cm or smaller. The cancer may also have spread to lymph nodes outside the peritoneum
• Stage IIIC – the cancer has spread to the peritoneum outside the pelvis and the cancer in the peritoneum is larger than 2 cm. The cancer may also have spread to lymph nodes outside the peritoneum or to the surface of the liver or spleen
• Stage IVA – the cancer has caused a build-up of fluid in the lungs (pleural effusion)
• Stage IVB – the cancer has spread to areas outside of the abdomen, such as the lungs or inside of the liver or spleen

Peritoneal metastases, or cancers that have spread from other areas of the body to the peritoneum, are considered advanced cancers and are classified as Stage IV in most instances based on the staging of their primary cancer type.