Exceptionally rapid response to pembrolizumab in a SMARCA4‐deficient thoracic sarcoma overexpressing PD‐L1: A case report

SMARCA4-deficient thoracic sarcoma (SMARCA4-DTS) is a new clinical entity characterized by SMARCA4 inactivation and has a dismal prognosis because of rapid growth. Effective treatments for SMARCA4-DTS have not yet been developed. Most recently, anti-programmed cell death 1 receptor (PD-1) blockade has been effective for SMARCA4-deficient lung cancer and malignant rhabdoid tumor-like tumors. Here, we describe a patient with SMARCA4-DTC who experienced a marked response to the administration of pembrolizumab. A 70-year-old female was referred to our department for treatment of SMARCA4-DTC. Positron emission tomography-computed tomography had revealed a left mediastinal tumor, peritoneal dissemination and multiple cutaneous metastases at diagnosis. Immunohistochemical analyses revealed 60% of tumor cells expressed programmed cell death ligand 1 (PD-L1). The patient was given pembrolizumab as first-line treatment. Pembrolizumab suppressed tumor growth dramatically, with only one dose leading to a partial response. Our case suggests the immunohistochemical analysis of PD-L1 expression be undertaken for patients with SMARCA4-DTS and that pembrolizumab treatment may be a promising strategy for PD-L1-positive SMARCA4-DTS.