Peritoneal Surface Malignancies
The peritoneum is the largest serous membrane in the body, and consists, in the male, of a closed sac, while in female the free ends of the uterine tubes open directly into the peritoneal cavity. The peritoneum differs from the other serous membranes of the body in presenting a much more complex arrangement. It is formed of two layers, one applied against the abdominal wall cavity (parietes) and called parietal peritoneum while the second is reflected over the contained organs (viscera) and called the visceral peritoneum. These reflections are named according to their function as ligaments, mesentery, omentum, bursa.
The free surface of the peritoneal membrane is smooth and lubricated by a small quantity of serous fluid allowing the abdominal viscera to glide freely against the wall of the cavity or upon one another with the least possible amount of friction. The attached surface is rough, being connected to the viscera and inner surface of the abdominal wall.
(Click here to see an image of the peritoneum and peritoneal membrane.)
Peritoneal surface malignancies, also called peritoneal carcinomatosis (PC), is the presence of cancer (malignant) cells on the surface of the peritoneum. The close relationship of the peritoneum to the abdominal organs can explain the frequency of direct extension of cancer originating from abdominal organs to the peritoneum. At the same time, its continuity and its serous fluid circulation can explain the frequency of the wide spread of the disease along its large surface area.
Where does this originate?
Tumors that originate from the peritoneum are rare (1-2/million per year) and are called primary peritoneal tumors. This category includes mesothelioma and primary peritoneal serous carcinoma. Mesothelioma of the peritoneum related to asbestos exposure is less defined than that of pleural mesothelioma. It is a difficult pathological diagnosis that can be wrongly labeled adenocarcinoma of unknown primary and extensive pathological workup with immunomarkers is essential for the diagnosis.
Most of the peritoneal tumors originally arise in another organ and secondarily extend to the peritoneal membrane. In the vast majority of cases, the origin of these tumors are intra-abdominal organs including the appendix, colon, rectum, stomach and ovaries. In 20 percent of abdominal malignancies, the only site of tumor recurrence remains intra-abdominal.
Ten percent of patients with colorectal cancer will develop peritoneal carcinomatosis at the same time of their diagnosis and 25 percent of remaining patients will develop peritoneal carcinomatosis later on in the disease process.
Appendiceal cancer is usually diagnosed in the postoperative setting with peritoneal spread. The peritoneal involvement in this case is either in the form of mucinous ascites with low grade adenomatous tumor (Diffuse peritoneal adenomucinosis or DPAM), or peritoneal deposit of mucinous carcinoma (Peritoneal mucinous carcinomatosis or PMCA). The two conditions can present clinically in the form of abundant mucinous ascitis and are called pseudomyxoma peritonei (PMP). Though clinically similar, DPAM and PMCA are different in their histology and their potential to spread to other organs. DPAM is characterized by the presence of abundant mucinous ascites with scant cells with minimal atypia and rarely spread to lymph nodes or other organs. On the other hand, PMCA presents with mucinous ascites and abundant cancerous cells and has the potential to spread to lymph nodes and distant organs. Both types cause abundant mucinous ascites that results in abdominal distention and pain and is the source of fibrosis that can cause bowel obstruction.
Other extra-abdominal organs such as the breast can also extend to the peritoneum.
How is this different from other kinds of GI cancer?
For a long time these tumors were classified as non-surgical because of the wide territory of the peritoneum membrane and the frequent extension of the disease to multiple intra-abdominal organs. Consequently, the possibility to achieve complete excision through a long, complex surgery involving resection of multiple abdominal organs was aborted due to the high risk and limited benefits of such an approach. At the same time, systemic intravenous chemotherapy had a little effect on the peritoneal tumors as the peritoneum membrane constitutes a compartment separate from the vascular compartment (the blood). Therefore, peritoneal tumors showed poor prognosis despite the best systemic therapy.
With the advance of the surgical techniques, equipment and postoperative care, the peritoneum is now considered an intra-abdominal organ that is can respond to surgery, called cytoreductive surgery (CRS). The development of the intraperitoneal route of heated chemotherapy administration (HIPEC) allows a direct contact between the tumor cells and the chemotherapeutic agent to control all residual microscopic disease. The development of CRS-HIPEC revolutionized the natural history of peritoneal tumors.
See answers to frequently asked questions about cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (HIPEC).