Metastatic and polytreated undifferentiated pleomorphic sarcoma with complete clinical and radiological response to Pembrolizumab: case report

Full text: Case presentation: P.F.S., male, 69 years old, with diagnosis of undifferentiated pleomorphic sarcoma in the thigh region. The lesion measured 9.7 cm on magnetic resonance imaging and had no evidence of lymph node involvement or distant metastasis. He underwent surgery and the anatomopathological and immunohistochemical study showed a 13 cm lesion, free surgical margins, 30% Ki67, and no expression of neurotrophic tyrosine receptor kinase (NTRK). After surgery, the patient received adjuvant chemotherapy with ifosfamide plus adriamycin (four cycles), followed by radiotherapy with a total dose of 60 Gy. Ten months after the end of the adjuvant treatment, metastatic bilateral pulmonary nodules of up to 0.7 cm appeared, infiltrating the visceral and unresectable pleura. Analysis of the lung sample revealed microsatellite stability and three mutations per megabase by the foundation one heme. He started chemotherapy with gemcitabine and docetaxel, having presented radiological progression with this regime and the other systemic treatments used in sequence: liposomal doxorubicin, eribulin, and pazopanib. Finally, with lung lesions of up to 1.8 cm, pembrolizumab was started and after seven months of immunotherapy showed an important radiological response, and full response in ten months. The patient is currently asymptomatic and has been using pembrolizumab for fifteen months, having presented only grade 1 cutaneous rash as toxicity. Discussion: Sarcomas are part of a heterogeneous group of tumors and treatment is increasingly being conducted according to histology, particularly in the setting of advanced disease. While surgical resection of the metastasis can provide increased relapse-free survival; in unresectable disease, palliative systemic therapy is performed to reduce tumor volume, reduce symptoms, improving quality of life, and prolonging survival. Pembrolizumab is one of the treatment options for advanced soft tissue sarcoma with microsatellite instability and high tumor mutational load. Final comments: The report in question draws attention to a case of advanced sarcoma with microsatellite stability and low tumor burden that had a clinical and radiological response to pembrolizumab, raising the question of the existence of other mechanisms involved in the response to immunotherapy in the treatment of sarcoma. (author)