Complete response to pembrolizumab in radiation-induced undifferentiated pleomorphic sarcoma of the face: A case report and review of the literature

Introduction: Undifferentiated pleomorphic sarcoma (UPS) as a secondary malignancy following adjuvant radiation therapy is rare and typically associated with poor prognosis. PD-1 inhibition has been previously investigated as a possible treatment in this space. Case Presentation: This case presents a 91-year-old male with UPS of the right parotid region, presumed secondary to radiation therapy for cutaneous squamous cell carcinoma. The patient was treated with pembrolizumab immunotherapy and a complete clinical response was achieved, with significant improvement noted on restaging scans. Treatment was well-tolerated despite advanced age and multiple comorbidities. Conclusion: This case demonstrates the efficacy of PD-1 inhibitor therapy in radiation-induced UPS and supports emerging evidence for immunotherapy as a viable treatment option in advanced or unresectable sarcomas, particularly with patients who cannot undergo surgery.