We describe a case of sarcomatous tumor of the chest wall with differentiation toward bone and cartilage that was observed in an asbestos-exposed worker. Although the mesothelial nature of the tumor was at first considered, it was not proven. Later, the tumor was shown to be a mesothelioma using a panel of pertinent antibodies that included a recently described anti-mesothelial cell marker. In addition, asbestos bodies were found in association with the sarcoma cells. Our findings indicate that whenever physicians encounter any type of primary sarcomatoid tumor involving serous membranes, the possibility of malignant mesothelioma should be regarded a priori.
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