Primary malignant mesothelial tumors in canada, 1960–1968.A pathologic review by the mesothelioma panel of the canadian tumor reference centre

Six pathologists reviewed 119 of 165 cases reported as primary malignant mesothelial tumors, between 1960 and 1968, in a Canadian national survey. Based on histologic observations only, the panel was in favor of the diagnosis in 50%, uncertain in 14%, and against in 36%. This distribution was similar for pleural and peritoneal tumors. In males, the diagnosis was favored more often than in females—61% compared to 26%. Clinical and additional pathologic information changed the pathologists' opinion little. A member of the UK Mesothelioma Panel who reviewed 44 of the 119 cases recorded essentially similar opinions. Subsequently, a further 71 cases were registered between 1968 and 1970, and reviewed pathologically. The 99 cases in all, in which the panel favored the diagnosis of malignant mesothelioma, had been exposed to asbestos slightly more frequently than the rest. Twelve of 26 (46%) tumors classified histologically as mixed were associated with asbestos exposure compared with 8 of 73 (11%) classified as epithelial or mesenchymal.