Pathologically mesothelioma is a difficult diagnosis to make. A combination of rarity of mesothelioma combined with the resemblance of this cancer to lung cancer results misdiagnosis of many cases that may be mesothelioma. Pathological opinion of same tumor may different as seen by different pathologist especially when litigation and compensation issues are involved. It is to be emphasized that a substantial fraction of mesothelioma occurs in people who were never been exposed to asbestos, and malignancies other than mesothelioma is common in those who have been exposed to asbestos. A diagnosis of mesothelioma may not be suspected in a person who has no history of exposure to asbestos, and a diagnosis of mesothelioma may be over-zealously explored in a person who gives history of significant exposure to asbestos. A diagnosis of mesothelioma should not be assumed just because of an exposure history to asbestos is present. It is very important to exclude other less aggressive diseases before making a diagnosis of mesothelioma because in general these may be more amenable to treatment than mesothelioma. Non-cancerous diseases like inflammatory and reactive processes can cause changes in the mesothelial cells and can resemble mesothelioma. Accurate diagnosis of mesothelioma is also very important in cases where litigation and attorneys are involved for compensation issues.
Several factors including measuring the levels of hyaluronic acid, hemopoietic growth factors, c-reactive protein, alpha one acid glycoprotein, fibronge and IL-6 have been suggested as useful tests in the diagnosis of mesothelioma. These tests may be added help in making the distinction between mesothelioma and lung cancer. These tests by itself are not specific for diagnosis of mesothelioma, but may be helpful together with biopsy, pathological examination, and imaging techniques.
Repeated biopsies of the pleura may yield negative results despite the presence of active mesothelioma. With the usual microscopic examination alone it may be difficult to distinguish mesothelioma from adeno-carcinoma of the lung. Electron microscopic examination may establish the diagnosis of mesothelioma. Bronchoscopy may help to locate a small occult primary lung cancer and may be thereby excluding the diagnosis of mesothelioma. Establishment of diagnosis of mesothelioma may require pathological examination of a biopsy of the pleura or e pleural fluid. Adeno-carcinoma originating in other parts of the body can involve pleura by metastatic spread, and it is important to exclude malignancies in these sites before making a definite diagnosis of mesothelioma. These sites from which an adeno-carcinoma can arise include lung, breast, ovary, pancreas, stomach, kidney, prostate, and gall bladder. It may be impossible to distinguish between adeno-carcinoma with extensive involvement of pleura and mesothelioma after extensive investigation. This condition where the adenocarcinoma of the lung causes extensive pleural involvement and mimic mesothelioma is termed as pseudo-mesothelioma. It may also be difficult to distinguish mesothelioma from fibrosarcomas, malignant fibrous histiocytomas, malignant swhannomas, hemangio-pericytomas, synovial sarcomas, and carcino-sarcomas.