All the organs in your abdomen are covered with a membrane called the peritoneum, which coats the organs like cling film. When bowel cancer grows through the bowel wall it can spread through the lymph glands and on to other organs such as the liver or it can spread in the peritoneum.
Cancer cells can break off from the main tumour and escape into the abdomen, implanting in the peritoneum on the surface of the organs and tissues that are contained there. Any organ in the abdomen and pelvis can be affected, but some tissues are particularly sensitive to this process. These are the omentum (fatty tissue between the stomach and the colon), the ovaries, the surface of the liver and the gutters beside the bowel above the pelvis.
Sometimes the spread involves tiny seedlings, widely distributed on the surface of the organs and bowel wall. The presence of peritoneal metastases does not always cause symptoms and it is more likely to be picked up during your routine tumour marker blood tests and CT scans.
The symptoms can be vague, but are likely to include unexplained pain, change in appetite or unexpected weight loss.On the other hand, weight gain can be caused by fluid collecting in the abdomen as a result of cancer cells that have spread there.
Investigations may include an ultrasound scan of the area, an abdominal CT scan or a PET scan. If a mass is identified in the pelvis, an MRI scan may also be useful. When bowel cancer spreads to the peritoneum, it can be more difficult to treat with standard chemotherapies. The treatment options available will depend on many factors, but in particular which organs are involved and whether those organs can be removed safely without affecting your quality of life.