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Peritoneal mesothelioma

Peritoneal mesothelioma is much less common than pleural mesothelioma and accounts for approximately 15% of cases. 

It is estimated that PM occurs in approximately 300 to 400 people in the US every year, but the true incidence may be higher as it may be misdiagnosed with other cancers involving the peritoneum.

Mean age is 69 years at diagnosis. 

One year overall survival approximately 46% and in five year overall survival about 20%. 

Cure is rare. 

Survival is improved by complete cyto reductive surgery with intraperitoneal chemotherapy. 

Histologic subtypes include epithelioid, the most common, sarcomatoid, and biphasic or mixed. 

While pleural mesothelioma is more common in males, there are equal numbers of males and females with plural mesothelioma. 

Patients with peritoneal mesothelioma are generally younger than patients with pleural mesothelioma.

Pleural mesothelioma is typically caused by asbestos exposure, but peritoneal mesothelioma is less frequently associated with asbestos. 

The incidence of pleural and peritoneal mesothelioma is decreasing because of decreased asbestos use. 

Patients present in an indolent fashion with abdominal pain, distention, ascites, and weight loss with a median time of 4 to 6 months between symptom onset and diagnosis.

Radical resection with cytoreductive surgery, and hyperthermia, intraperitoneal chemotherapy are the primary curative measures for malignant peritoneal mesothelioma,and the strongest predictor of long-term survival is complete removal of all visible disease.

Cytology has limited sensitivity for diagnosis, ranging from 30 to 75% and is not recommended for diagnosis.

Adequate biopsy is recommended for histologic diagnosis and immunohistochemistry. 

Such biopsies can be attained at the time of diagnostic laparoscopic exam or by image guided biopsy in the setting of a mass.

Sarcomatoid subtype accounts for 20% of cases, and has more aggressive disease process, with local invasion, and spread beyond the peritoneal cavity.

Sarcomatoid subtype has a universal poor prognosis with prompt recurrences and immediate survival of less than six months, and is a contraindication to curative intense surgery.

Evaluation includes CT of the chest, abdomen and pelvis at the time of diagnosis and findings can help rule out bicavity involvement, which is a relative comfort indication for upfront surgery. 

The presence of metastatic lymphadenopathy has a poor prognosis and is present in 7 to 13% of patients.

Imaging studies often underestimate the peritoneal cancer index, the extent of disease for prognosis and operability.

The studies are important, however, to avoid unresectable disease and non-therapeutic laparotomy.

Genetic factors play a role in some patients with families carrying the germline mutation in the BRCA, 1 associated protein– one gene, and a few patients with somatic mutation, such as anaplastic lymphoma kinase (ALK) rearrangements.

Patient presents with abdominal signs and symptoms: ascites(77%) pain (69%), distention, and abdominal mass (30%).

Patients frequently have weight loss, fatigue, anorexia, asthenia, and nausea, along with early satiety and intestinal obstruction.

Diagnosis may be delayed because of non-specific symptoms.

Many patients have advanced disease at diagnosis with extensive intraabdominal spread, and commonly the disease metastasizes beyond the abdominal cavity.

Diagnosis evaluation include CT examination of the chest, abdomen and pelvis, and laparoscopic exam to obtain a biopsy of the mass or nodules.

Fine needle, aspiration, and paracentesis are not adequate for diagnosis.

Measurement of soluble, mesothelin related peptide and CA125 levels are considered.

Tissue biopsy is essential for accurate diagnosis as other studies are not specific.

Localized, peritoneal mesothelioma is extremely rare.

Epithelioid subtype peritoneal mesothelioma has a median survival of 39 months compared with biphasic subtype of 14 months. 

The median survival is of patients is improved if they can undergo cytoreductive surgery.

For diagnosis, the lesion needs to be diffuse, mesothelial, and malignant. 

There is no single immunohistochemistry marker for diagnosis.

Positive markers include calretinin  and podoplanin.

BAP1, a tumor suppressive gene loss is a useful molecular marker for diagnosing mesothelioma.

MANAGMENT:

Treatment options for diffuse, peritoneal mesothelioma include surgery and/or systemic therapy.

Radiation is reserved for selective patients for palliation.

Cytoreductive surgery and intraperitoneal chemotherapy are standard approaches for patients eligible for surgery.

Surgery is typically contraindicated with bicavity disease and those with biphasic or  sarcomatoid histology.

Complete cytoreduction is recommended for patients with epithelioid histology and unicavity  peritoneal mesothelioma who are medically operable.

Complete macroscopic resection, while removing all visible or palpable tumors frequently involves a total peritonealectomy.

Cytoreductive surgery should be aborted if it is not possible to have a complete or near complete cytoreduction.

In patients with complete cytoreduction and hyperthermia inta5 peritoneal chemotherapy, the overall median survival was 53 months with three and five years survival rates of 60 and 47% respectively.

Intraperitoneal agents include cisplatin, doxyrubicin, or mitomycin C.

Systemic therapy regimens are considered for patients with mesothelioma who are not eligible for surgery and include agents like platinum and pemetrexed.

Evidence exists for the use of checkpoint inhibitors.

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