Peritoneal mesothelioma, a cancer of the lining of the abdominal cavity, is less common than the pleural form, comprising approximately one-fifth to one-third of the total number of mesothelioma cases diagnosed. According to the SEER (Surveillance, Epidemiology, and End Results) database, these diagnoses are approximately 54.7 per cent male versus 45.3 per cent female, with the median age being 65-69. The latency period appears to be shorter for asbestos-exposed individuals with symptoms appearing 20-30 years after exposure rather than the 30-40 year latency more commonly associated with pleural mesothelioma.
Clinical symptoms at the time of presentation may include abdominal pain, abdominal mass, increased abdominal girth, distention of the abdomen, ascites (fluid in the abdomen), fever, weight loss, fatigue, anemia and digestive disturbances. Some patients complain of more non-specific symptoms for a number of months prior to a confirmed diagnosis. In a percentage of cases, peritoneal mesothelioma is found incidentally when the patient has sought help for another health problem such as gallbladder, hernia or pelvic mass.
Experienced doctors report that patients typically experience symptoms 6 months to 2 years before diagnosis. When the patient goes to the doctor, the patient, the family, and the doctor all usually think something else is wrong. Men often first show up with an inguinal hernia (a bulge in the groin) or an umbilical hernia (bulge around the belly button.) The first indication of a problem for some women comes during a pelvic examination when a tumor mass is discovered.
Late-stage peritoneal mesothelioma symptoms include bowel obstruction and increased tendency of the blood to clot. Blood tests show increased platelet count in half of peritoneal patients, although this is of little use in diagnosis because it can be caused by so many disorders. Anemia and low albumin levels are also found.
As with all mesotheliomas, the diagnosis of peritoneal mesothelioma can be challenging. CT findings may help differentiate between the two clinical types of peritoneal mesothelioma, termed “dry” or “wet”, since their appearances are very different upon imaging. In the “dry” type, CT may reveal multiple small masses or a single dominant localized mass. There is normally little or no ascites. In the “wet” type, CT may reveal widespread small nodules, but no dominant mass. Ascites is usually present.
If fluid is present, it may be removed in a procedure called paracentesis. Unfortunately, as is the case with pleural mesothelioma, fluid analysis offers limited diagnostic value. It is normally a tissue biopsy obtained in a laproscopic exploratory that will yield a definitive diagnosis.
There is currently no established staging system for peritoneal mesothelioma, and if the disease is staged, it is normally done in accordance with the TNM system, the most common general cancer staging system. This system refers to the status of the tumor (T), lymph nodes (N) and metastases (M). There are general categories which may also be somewhat helpful in determining stage.
The first category shows a localized lesion able to be completely resected (entirely removed). In the second category, the disease is contained within the abdominal cavity on peritoneal and organ surfaces where debulking (the removal of as much, but not all of the tumor) is possible. Category three shows disease contained within the abdominal cavity with invasion of organs such as the colon or liver. Category four shows disease extending outside the abdominal cavity.
Mesothelioma specialist Clare Verschraegen wrote that she categorizes peritoneal mesothelioma into four categories. The least developed is when the tumor has not spread and can be removed with surgery. This is equivalent to stage I in the Butchart classification.
The next is when the cancer has spread to the periconal and organ surfaces and surgery will result only in a debulking of the tumor, not removal of all malignant tissue. The next stages are when the cancer metasticises to other organs, and when it gets into the lymph nodes.
In recent years, multimodality treatment of peritoneal mesothelioma has become more common for a select patient population, since surgery alone and/or intraperitoneal chemotherapy alone have proven to be similarly ineffective. Cytoreductive (debulking) surgery involves the removal of all or nearly all visible tumor, and, depending on the physician’s choice, may be combined with Intra-Peritoneal Hyperthermic Chemotherapy (IPHC), intraperitoneal chemotherapy and/or radiation. Dr. Paul Sugarbaker has written “intraperitoneal chemotherapy gives high response rates within the abdomen because the peritoneal space to plasma barrier provides dose intensive therapy.” Since it is not always possible to remove all tumors, the prognosis for long-term survival may be based on the completeness of cytoreduction as established by the following criteria:
CC-0 No peritoneal seeding is visualized within the operative fields.
CC-1 Nodules of less than 2.5 cm persist after cytoreduction. Nodules of this size are thought to be penetrable by intracavitary chemotherapy, therefore cytoreduction is termed complete.
CC-2 Nodules of between 2.5 and 5 cm persist after cytoreduction.
CC-3 Nodules of greater than 5 cm or a merging of unresectable tumor nodules at any site within the abdomen or pelvis.
For patients found to have widespread disease, where surgery is not looked at as “potentially curative”, palliation of symptoms may be accomplished by debulking. Since peritoneal mesothelioma is a rare malignancy, specialized treatments should be conducted by doctors familiar with the disease.
A recent clinical trial found pemetrexed (Alimta) to be an effective chemotherapy agent in treatment of peritoneal mesothelioma, either along or with a platinum-based drug such as cisplatin. This success mirrors previous findings about pemetrexed for treatment of pleural mesothelioma.
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