TY - JOUR AB - Histiocytic sarcoma (HS) is a rare hematological malignancy, which exhibits morphological and immunophenotypic features of histiocytes. A standard therapy for HS has not yet been established due to its rareness; therefore, disease control is not always possible. A multimodal treatment strategy has been suggested for HS. The present study reported on a case of a 43‑year‑old female patient who complained of left femoral pain, which was caused by left femoral bone mass. A biopsy of their left femoral bone tumor revealed that the patient had HS. Their sarcoma was localized in the femoral bone and was not considered to be curable, due to local infiltration of the bone tumor beyond the periosteum. The patient then underwent two types of HS‑specific chemotherapy; however, both regimens were ineffective. As a result, they underwent radiation therapy at the sites of progressive disease. Because the HS cells of the patient expressed PD‑L1, they were treated with nivolumab (240 mg/body, biweekly) for residual diseases in the right occipital bone, multiple lung nodules, intrapelvic right lymph node and primary site. Nivolumab treatment resulted in a complete response at all sites, with the exception of the primary site, which was confirmed by 18F‑fluorodeoxyglucose‑positron emission tomography/computed tomography. The patient received additional nivolumab treatment as consolidation therapy for 1 year. In addition, residual disease of the femoral head was completely resected. The surgically resected refractory tumor revealed the tumor cells no longer pathologically expressed PD‑L1 . In conclusion, for refractory and recurrent HS in which surgical resection is not appropriate, treatment with immune‑checkpoint inhibitors, such as nivolumab, may be considered an optional but promising immunotherapy if the tumor histologically expresses PD‑L1. The present study detected one of the refractory mechanisms of ICI treatment. AD - Division of Hematology, Department of Internal Medicine, Faculty of Medicine, Kagawa University, Miki, Kagawa 761‑0793, Japan AU - Imataki,Osamu AU - Uemura,Makiko AU - Fujita,Haruyuki AU - Kadowaki,Norimitsu DA - 2022/09/01 DO - 10.3892/mco.2022.2569 IS - 3 JO - Mol Clin Oncol KW - histiocytic sarcoma PD‑L1 immune‑checkpoint inhibitor nivolumab resistance mechanism 18F‑FDG‑PET PY - 2022 SN - 2049-9450 2049-9469 SP - 136 ST - Application of PD‑L1 blockade in refractory histiocytic sarcoma: A case report T2 - Molecular and Clinical Oncology TI - Application of PD‑L1 blockade in refractory histiocytic sarcoma: A case report UR - https://doi.org/10.3892/mco.2022.2569 VL - 17 ER -