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.