[Dedifferentiated liposarcoma of the omentum simulating malignant peritoneal mesothelioma]

Liposarcoma of the omentum is a rare tumour which can simulate mesothelioma by naked eye and in histology as it was in the described case: A diffuse tumorous infiltration of parietal and visceral peritoneum was found in a male autopsy combined with two secondaries in the liver and one renal. The omentum was increased and quite infiltrated by the tumour. Single tumour foci consisted of structures reminding of a malignant neurogenous tumour, malignant fibrous histiocytoma and haemangiopericytoma. Some areas with a rather oval tumour cells with poor cohesivity reminded of a malignant lymphoma but were without any immunohistochemical positivity with markers proper for ML. A series of other tumours were to be eliminated in differential diagnostic consideration, i.e. sarcomatoid carcinoma, GIST, secondaries of a sarcomatoid variant of melanoma, malignant schwannoma, malignant fibrous histiocytoma, peritoneal leiomyomatosis. The prevalence of dedifferentiated structures can mostly veil the diagnosis of liposarcoma and immunohistochemical results are not always constant. A transition between well differentiated liposarcoma and its dedifferentiated structures are to be found in a single section for correct diagnosis. Prognosis of the dedifferentiated liposarcoma is presumed to be better than that of pleiomorphic sarcomas. The described patient was presented in terminal stage of disease and was monitored but for a month.