Undifferentiated pleomorphic sarcoma (ORPHA:2023)
An aggressive sarcoma of soft tissues or bone that can arise from any part of the body, clinically presenting as swelling, mass, pain, pathological fracture and occasional systemic features and is characterized by high local recurrence and significant metastasis.
Epidemiology
UPS ranks the 4th most common soft tissue sarcoma with a slight male preponderance. The incidence has been evaluated to be close to 0.8-1 new case per 100000 per year in one European series.
Clinical description
The tumor arises most commonly during the sixth and seventh decades of life. The most common sites of involvement include lower extremities (mainly thigh) followed by upper arms, retroperitoneum, viscera, head and neck (in childhood). Primary osseous UPS most commonly occurs in distal femur, proximal tibia, proximal femur and humerus. Patients may present pain, swelling / mass and pathological fractures. In the skin, UPS presents as a relatively painless, rapidly enlarging nodule. Anorexia, malaise, fever and weight loss are present in retroperitoneal and inflammatory forms of UPS. Most UPS recur locally; distant metastases are common (the most frequent is lung). Regional metastases are rare.
Etiology
UPS is thought to be derived from a primitive mesenchymal cell capable of differentiating into histiocytes, fibroblasts, myofibroblasts and osteoclasts. The etiology of the tumor remains unknown. Prior radiation therapy is a likely risk factor in some cases.
Diagnostic methods
Any tumor mass over 5 cm is suspected to be a sarcoma. Magnetic resonance imaging (MRI) is the imaging method of choice for limbs and shows a high signal on T2 weighted images. Histology of biopsy specimen prior to any treatment is crucial to reach diagnosis and shows pleomorphic spindle cell population with large atypical cells frequently exhibiting numerous irregular mitotic figures, associated regions of hemorrhage and necrosis, associated lymphohistiocytic infiltrate and invasion of dermis. Immunohistochemical staining is negative for S-100, HMB-45, CD34 and cytokeratin which assists in ruling out other soft tissue tumors. Most cases previously diagnosed as malignant fibrous histiocytoma have been reclassified into other histological types of sarcoma.
Differential diagnosis
When occurring in skin, UPS is difficult to differentiate from atypical fibroxanthoma or dermatofibrosarcoma protuberans (see this term). Histological differential diagnoses include leiomyosarcoma, rhabdomyosarcoma, lymphoma, and melanoma (see these terms).
Management and treatment
UPS should be referred to an expert/ reference center for primary biopsy, expert pathology review, and multidisciplinary treatment. Immediate surgery of a mass without knowledge of its histological nature is strongly discouraged because it is associated with an increased risk of death due to inappropriate resection and increased risk of relapse. UPS is best treated by wide surgical excision. Sometimes amputation may be necessary to remove the whole lesion. Adjuvant radiotherapy is given for high-grade, large (>5 cm), deep-seated tumors, in limb sparing surgeries and when negative margins are not obtained. For non-operable sarcomas, primary radiation therapy could be an option, but usually doxorubicin containing regimens are preferred options in first-line setting for locally irresectable and/or metastatic lesions. Chemotherapy (CHT) with ifosfamide, trabectedin, dacarbazine, pazopanib have demonstrated efficacy in UPS and are registered and available in most European Union countries.
Prognosis
A 5-year overall survival rate of 48% has been reported for patients with head and neck tumors versus 77% for patients with tumors arising on the trunk and extremities. The childhood variant appears have better prognosis.

                            Last update: 
                            June 2014


                            - Expert reviewer(s): 
                            Pr Jean-Yves BLAY