This is supported by the observed recruitment of significant numbers of macrophages and other cells of the immune system to localized lesions of accumulated asbestos fibers in the pleural and peritoneal cavities of rats. These lesions continued to attract and accumulate macrophages as the disease progressed, and cellular changes within the lesion culminated in a morphologically malignant tumor.Experimental evidence suggests that asbestos acts as a complete carcinogen with the development of mesothelioma occurring in sequential stages of initiation and promotion. The molecular mechanisms underlying the malignant transformation of normal mesothelial cells by asbestos fibers remain unclear despite the demonstration of its oncogenic capabilities (see next-but-one paragraph). However, complete in vitro transformation of normal human mesothelial cells to a malignant phenotype following exposure to asbestos fibers has not yet been achieved. In general, asbestos fibers are thought to act through direct physical interactions with the cells of the mesothelium in conjunction with indirect effects following interaction with inflammatory cells such as macrophages. Intracellular
Analysis of the interactions between asbestos fibers and DNA has shown that phagocytosed fibers are able to make contact with chromosomes, often adhering to the chromatin fibers or becoming entangled within the chromosome. This contact between the asbestos fiber and the chromosomes or structural proteins of the spindle apparatus can induce complex abnormalities. The most common abnormality is monosomy of chromosome 22.
Epithelioid and biphasic mesothelioma make up approximately 75-95% of mesotheliomas and have been well characterized histologically, whereas sarcomatous mesothelioma has not been studied extensively. Most mesotheliomas express high levels of cytokeratin 5 regardless of subtype.Epithelioid mesothelioma is characterized by high levels of calretinin.Sarcomatous mesothelioma does not express high levels of calretinin.Other morphological subtypes have been described:

Desmoplastic
Clear cell
Deciduoid
Adenomatoid
Glandular
Mucohyaline
Cartilaginous and osseous metaplasia
Lymphohistiocytic

Differential diagnosis
Metastatic adenocarcinoma
Pleural sarcoma
Synovial sarcoma
Thymoma
Metastatic clear cell renal cell carcinoma
Metastatic osteosarcoma

Staging
Staging of mesothelioma is based on the recommendation by the International Mesothelioma Interest Group. TNM classification of the primary tumor, lymph node involvement, and distant metastasis is performed. Mesothelioma is staged Ia–IV (one-A to four) based on the TNM status. Prevention
Mesothelioma can be prevented in most cases by preventing exposure to asbestos. The US National Institute for Occupational Safety and Health maintains a recommended exposure limit of 0.1 asbestos fiber per cubic centimeter. Screening
There is no universally agreed protocol for screening people who have been exposed to asbestos. Screening tests might diagnose mesothelioma earlier than conventional methods thus improving the survival prospects for patients. The serum osteopontin level might be useful in screening asbestos-exposed people for mesothelioma. The level of soluble mesothelin-related protein is elevated in the serum of about 75% of patients at diagnosis and it has been suggested that it may be useful for screening. Doctors have begun testing the Mesomark assay, which measures levels of soluble mesothelin-related proteins (SMRPs) released by mesothelioma cells. Treatment
Mesothelioma is generally resistant to radiation and chemotherapy treatment. Long-term survival and cures are exceedingly rare.