Undifferentiated pleomorphic sarcoma of the retroperitoneum
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Undifferentiated pleomorphic sarcomas (UPS), previously known as malignant fibrous histiocytoma (MFH), are an uncommon tumor overall but are considered as one of the most common types of primary retroperitoneal neoplasms.
For a broad discussion of this type of a tumor, which commonly involves the extremities, please refer to the main article on undifferentiated pleomorphic sarcoma.
Retroperitoneal malignant fibrous histiocytomas correspond to approximately 15% of all UPS 3. They occur with predominance in men.
They are categorized as sarcomas and are often high-grade tumors.
There are six histological subtypes: storiform, pleomorphic, myxoid, giant cell, inflammatory and angiomatoid. Most metastasize and common sites include lung and lymph nodes.
Imaging is not characteristic and clarification pathologically is required. Reassessment of a UPS diagnosis in some series result in re-classification as dedifferentiated liposarcomas.
25% of cases include dystrophic calcification which is uncommon amongst the remaining primary retroperitoneal malignancies.
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