Undifferentiated pleomorphic sarcoma is an acquired malignancy and is not inherited from parents in a Mendelian fashion. The tumor arises from genetic changes that occur in soft tissue cells during a person's lifetime rather than from variants passed down through families, and the genetic basis is under investigation. Recognized risk factors include prior therapeutic radiation to the affected region, longstanding lymphedema, and exposure to certain chemicals; in a small minority of cases, a soft tissue sarcoma may arise in the setting of a rare hereditary cancer predisposition syndrome, but most cases occur sporadically without an identifiable familial cause.

Evaluation begins with imaging of the affected region, with magnetic resonance imaging considered the standard for characterizing a soft tissue mass and defining its relationship to surrounding structures. Diagnosis is confirmed by tissue sampling, typically image-guided core needle biopsy performed in coordination with a sarcoma-experienced multidisciplinary team. A specialized soft tissue pathologist reviews the histology and applies immunohistochemical stains to exclude other sarcoma subtypes before assigning the diagnosis. Staging generally includes computed tomography of the chest to screen for pulmonary metastases, with additional cross-sectional imaging as clinically indicated. Symptoms of undifferentiated pleomorphic sarcoma can overlap with other conditions, including dedifferentiated liposarcoma, malignant peripheral nerve sheath tumor, melanoma, and other high-grade pleomorphic sarcomas. Histopathology and immunohistochemistry are required to confirm the diagnosis and distinguish it from conditions with similar presentations.

Treatment planning depends on disease stage, tumor size and location, grade, and overall health. Management often involves a multidisciplinary oncology team that includes surgical oncology, medical oncology, radiation oncology, and sarcoma pathology, and may include surgery, local therapies, systemic treatment approaches, and supportive care. For localized disease, wide surgical excision aiming for negative margins is generally the cornerstone of curative-intent therapy. Radiation therapy may be offered before or after surgery to improve local control, particularly for larger, deeper, or higher-grade lesions. Treatment goals are individualized and may focus on disease control, symptom management, or curative intent depending on the specific situation. Patients should discuss treatment options with their healthcare team to determine which therapies may be appropriate for their specific situation.

Outcomes in undifferentiated pleomorphic sarcoma are variable and depend on stage at diagnosis, tumor size and depth, histologic grade, anatomic location, and response to treatment. Localized disease that can be completely resected with negative margins is generally associated with more favorable outcomes than locally advanced or metastatic disease. With advances in surgical technique, radiation planning, and integration of care at experienced sarcoma centers, survival outcomes have improved over time. Early detection and access to specialized oncology care can improve outcomes.

Active research into undifferentiated pleomorphic sarcoma includes numerous ongoing clinical trials spanning combination immunotherapy, targeted agents, novel radiation strategies, and locally directed therapies. Notable studies include a Phase 3 National Cancer Institute trial evaluating whether the addition of immunotherapy to chemotherapy improves outcomes for aggressive poorly differentiated sarcomas, and Phase 2 trials examining checkpoint inhibitor combinations and preoperative radiation approaches in soft tissue sarcoma. Individuals interested in clinical trials can search ClinicalTrials.gov or consult their care team about eligibility.