Malignant mesotheliomas are divided into three histological subtypes: epithelial, sarcomatous, and mixed or biphasic. These patterns are found in roughly 55%, 15%, and 30% of cases. In general terms the behaviour of epithelial mesotheliomas is similar to that of carcinomas with local spread, large pleural effusions, and metastases to regional lymph
nodes. Sarcomatous mesotheliomas are associated more frequently with distant metastases,
little or no effusion, and shorter survival. Mixed mesotheliomas have intermediate features.
Among the biphasic and sarcomatous subtypes is a group of tumours in which more than 50% of the tumour consists of dense, hypocellular collagenous tissue. These tumours have been termed desmoplastic malignant mesothelioma (DMM). In these studies, and in our own, there was a predominance of sarcomatous mesotheliomas (sarcomatous DMM). Unlike Cantin, we found no real difference in survival between cases of sarcomatous DMM (5-8 months) and biphasic DMM (6-8 months). Hillerdal, in a review of 4710 published cases of mesothelioma, found the survival in sarcomatous and biphasic types to be five and 11 months, respectively. The prognosis of our biphasic group with desmoplasia was similar to that of sarcomatous mesotheliomas.