+ Pathophysiology
- Mesothelioma is rare
- Mesothelioma is a tumor arising from mesothelial cells of the pleural and peritoneal cavities
- Sites: thoracic cavity, pericardium, abdominal cavity, and vaginal tunic of the scrotum
- Etiology: congenital form and secondary to asbestos
- Asbestos is a complete carcinogen, initiator, tumor promoter, and causes chromosomal damage
- Asbestos is composed of chrysotile and amphibole fibres
- Amphibole fibres are responsible for the increased risk of mesothelioma
- Histologic types of mesothelioma: epithelial (most common), mesenchymal, and mixed
- Epithelial mesothelioma resembles carcinoma or ADC
- Mixed mesothelioma (= sclerosing mesothelioma): male dogs and GSD are over-represented
- cystic mesothelioma has been reported in 1 dog
+ Clinical Signs
- Pleural and peritoneal effusion are the most common presenting signs
- Extensive effusion due to exudation from tumor surface and tumor-obstructed lymphatics
- Acute tamponade and right-sided heart failure with pericardial mesothelioma
- Sclerosing mesothelioma: restrictive disease resulting in vomiting and urinary disease
+ Diagnosis
- Ultrasonography and survey radiographs are not usually useful as diffuse disease is more common than space-occupying lesions
- Mesothelial cells can exfoliate under many circumstances resulting in difficulty differentiating physiologic mesothelial cell proliferation from neoplasia
- Pericardial fluid pH may differentiate benign and malignant effusions with pH in dogs mesothelioma and HSA > 7.5 while benign effusions have a pH < 6.5
- Fibronectin concentration are increased with neoplasia (sensitive but not specific)
- Definitive diagnosis: histopathology ± immunohistochemistry
+ Treatment
- Pericardiectomy provides palliation for animals with cardiac tamponade
- Intracavitary cisplatin: well-tolerated with decreased fluid accumulation
- Intracavitary cisplatin combined with systemic chemotherapy may be promising
- Intracavitary cisplatin results in resolution of effusion after 1-2 doses with DFI ranging from 129 days to 27 months
+ Prognosis
- MST 13.6 months for pericardial mesothelioma following pericardiectomy, with 1-year survival rate 80% and 2-year survival rate 40%
- Recurrent pleural effusion > 30 days after pericardiectomy associated with a worse prognosis and < 120 days more likely to be associated with mesothelioma