Favorable outcome of a histiocytic sarcoma patient treated with immune checkpoint inhibitor: a case report

Abstract

Introduction and importance: Histiocytic sarcoma (HS) is an extremely rare malignancy in which there has been no standard treatment approach. Some preclinical studies have provided rationales for the application of immunotherapy in advanced HS. Case presentation We reported a case of a 61-year-old patient with metastatic HS who had a rapid progression on ifosfamide, carboplatin and etoposide chemotherapy. We performed PD-L1 testing which showed a strong positivity in 90% of tumor cells. The patient was then treated with pembrolizumab 200 mg every 3 weeks. He refused palliative radiotherapy. A dramatic response in all sites was recorded on PET-CT scan after 3 cycles. He was maintained on pembrolizumab, reaching over 30 months without disease progression. Clinical Discussion Recent molecular data suggests there could be a role of immunotherapy in histiocytic sarcoma. In our patient, the disease was refractory to chemotherapy and pembrolizumab has been given based on the strong PD-L1 expression. Response to immunotherapy has also been recorded in several cases with malignant histiocytic neoplasm. Conclusion Immunotherapy might bring sustained disease remission in PD-L1 high expression HS and further studies evaluating the role of immune checkpoint inhibitor in this disease are warranted.