Undifferentiated pleomorphic sarcoma

Undifferentiated pleomorphic sarcoma (UPS), formerly known as malignant fibrous histiocytoma (MFH), is a rare and aggressive soft tissue sarcoma that does not show a specific line of cellular differentiation when examined under the microscope. It is one of the most common soft tissue sarcomas diagnosed in adults, typically arising in the deep soft tissues of the extremities (especially the thigh), the retroperitoneum (the area behind the abdominal cavity), and less commonly in other locations such as the trunk or head and neck region. The tumor is classified as 'undifferentiated' because the malignant cells lack identifiable features that would assign them to a specific tissue type such as muscle, fat, or nerve. Patients typically present with a painless or mildly painful enlarging mass that may grow rapidly over weeks to months. Depending on the tumor's location, symptoms can include swelling, limited range of motion, compression of nearby nerves or blood vessels, and in retroperitoneal cases, abdominal discomfort or fullness. UPS has a significant potential for local recurrence and distant metastasis, most commonly to the lungs. Constitutional symptoms such as fatigue and weight loss may occur in advanced disease. Treatment of undifferentiated pleomorphic sarcoma generally involves a multimodal approach. Wide surgical excision with adequate margins is the cornerstone of therapy. Radiation therapy is frequently used as an adjunct, either before or after surgery, to reduce the risk of local recurrence. Chemotherapy, often with doxorubicin-based regimens, may be considered for high-grade tumors, large tumors, or metastatic disease, though its overall benefit remains a subject of ongoing research. Prognosis depends on factors including tumor size, depth, grade, location, and the presence of metastases at diagnosis. Five-year survival rates vary but are generally in the range of 50–70% for localized disease. Clinical trials investigating targeted therapies and immunotherapy are ongoing and represent areas of active research.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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