6, 7, 8 We consider the correct diagnosis to be imperative because of the different prognostic implications of other disorders that mimic sarcomatoid malignant mesothelioma (eg, desmoplastic malignant mesothelioma vs fibrous pleuritis), including the choice of treatment regimes (eg, sarcomatoid malignant mesothelioma vs pleural synovial sarcoma), and because of the medicolegal implications. Histological diagnosis of sarcomatoid malignant mesothelioma-notably the desmoplastic and lymphohistiocytoid subtypes-can be more problematic than for epithelioid or biphasic malignant mesotheliomas, because of similarity with benign fibrous pleuritis in the case of desmoplastic malignant mesothelioma, and with non-mesothelial tumors such as malignant fibrous histiocytoma and even non-Hodgkin's lymphoma, and because of restricted or inconsistent expression of mesothelial markers on immunohistochemistry. Prognosis is poor for all malignant mesotheliomas, but sarcomatoid malignant mesotheliomas have a particularly poor response rate to treatment, with a median survival of 6 months in one study, 5.8 months in another, 5.5 months for cases in the German Mesothelioma Register, and 6.2 months survival for desmoplastic malignant mesotheliomas. 1 This classification has implications for both diagnosis and prognosis. The World Health Organization classifies malignant mesothelioma into epithelial, sarcomatoid, and biphasic types, each of which can be subdivided further. The causal relationship to past inhalation of asbestos fibers-especially amphibole asbestos-is well recognized, and despite bans or restrictions on the use of asbestos, malignant mesothelioma will continue to represent a significant public health problem for many years to come, because of the long latency interval between the commencement of exposure and the subsequent malignant mesothelioma. Primary tumors of the pleura are rare overall, and diffuse malignant mesothelioma is the most common of these neoplasms. The relationship with asbestos exposure-particularly amosite-and an association with pleural plaques and less often asbestosis is confirmed.
#326 e high s series#
This study represents the largest series of sarcomatoid and desmoplastic malignant mesotheliomas to date and confirms the diagnostic usefulness of CK immunohistochemistry. Amosite fibers were the most commonly identified fibers using energy-dispersive X-ray analysis and were significantly higher in the sarcomatoid cases, as were uncoated fibers using scanning electron microscopy. The median asbestos body count was 1640/g wet lung tissue (by light microscopy). Fiber analysis was performed in 61 cases. Pleural plaques were present in 79% of cases for which information was available, and asbestosis was diagnosed in 34/127 cases (27%). Labeling for cytokeratins (CKs) was observed in 261/280 cases (93%), and for calretinin and vimentin in 31 and 91%, respectively. Rare subtypes included two cases with a lymphohistiocytoid pattern (<1%) and eight heterologous mesotheliomas (2%). Some desmoplastic features were identified in 110 cases (34%), and 70 (21%) were classified as desmoplastic. Most tumors were pleural (319 98%), and 7 were peritoneal (2%). Patients included 312 men (96%) and 14 women (4%), with a median age of 70 years (range 41–94 years). This study comprises 326 cases of sarcomatoid mesotheliomas among 2000 consecutive malignant mesothelioma cases received in consultation (16%). Sarcomatoid mesothelioma is the least common, but most aggressive of the three major histological types of mesotheliomas.