Mesothelioma is a highly aggressive tumor that carries a very poor prognosis. It predominantly arises from the pleura, whereas the peritoneum is the second important location. Typical symptoms are nonspecific, such as a nonproductive cough, dyspnea, and localized chest pain in the case of pleural mesothelioma, whereas abdominal pain, anorexia, weight loss, and swelling of the abdomen are reported with peritoneal tumors. The diagnosis rests on a thorough clinical assessment, imaging studies, and a biopsy followed by a histopathological examination and immunohistochemical staining.
The clinical presentation of mesothelioma is rather insidious and a very late diagnosis is made in most patients due to the nonspecific nature of complaints  . It is established that up to 4 months pass from the onset of symptoms before the tumor is recognized , which significantly reduces survival rates. Mesotheliomas are much more likely to occur in men, primarily due to its association with occupational exposure to asbestos and other known carcinogens (the male-to-female ratio is established at 5:1)  . The clinical presentation depends on the location of the tumor, with the two main locations being the pleura (the most common) and the peritoneum    . In the majority of cases suffering from pleural mesothelioma, a nonproductive cough that is often accompanied by dyspnea, fatigue, diaphoresis, and focal chest pain in some people are notable complaints   . Rarely, scoliosis toward the ipsilateral side or splinting may develop due to the expansive nature of the tumor . Conversely, abdominal pain, swelling, anorexia, profound losses in body weight, as well as ascites are manifestations of peritoneal mesothelioma . In some patients, the diagnosis is made incidentally .
The diagnostic workup should start with a meticulous clinical assessment. A detailed history must cover the onset of symptoms and their progression, as well as occupational details and whether exposure to asbestos or other harmful chemicals exists. During the physical examination, dullness on percussion due to a pleural effusion or diminished breathing sounds may be detected in the case of pleural mesotheliomas , in which case imaging studies need to be employed. Although plain radiography is a useful first-line study for the evaluation of the chest, more advanced studies, such as computed tomography (CT), magnetic resonance imaging (MRI), endoscopic ultrasonography (EUS), mediastinoscopy, laparoscopy, and positron emission tomography (PET) are recommended, primarily because they are able to determine the stage and aid in designing the optimal therapeutic strategy    . To make a definite diagnosis, however, a sample of the tumor must be obtained for a histopathological examination. Because pleural cytology is not useful in the case of mesothelioma, fine-needle aspiration biopsy (FNAB), often guided by CT, or video-assisted thoracoscopy (which shows superior results compared to FNAB) are viable techniques that are used in practice  . Immunohistochemical staining should include calretinin, as it carries a sensitivity rate of 95% and a specificity rate of 87% . Other important markers are cytokeratin, mesothelin, and D2-40   .