Tumor regression after combination of radiation and PD-1 antibody nivolumab treatment in a patient with metastatic mediastinal leiomyosarcoma: a case report.

The PD-1/PD-L1 axis is characterized as an important checkpoint of immune activation, particularly through negatively regulating T cell function. Although accumulated evidence has demonstrated the patients with some types of tumor benefit from blockade of PD-1/PD-L1 signaling pathway, the possible synergistic effect of combination of radiotherapy and anti-PD-1/PD-L1 antibody still need to be explored. Here, we report a case of patient who was diagnosed with metastatic mediastinal leiomyosarcoma and treated by combination of local radiotherapy and anti-PD-1 antibody nivolumab. Remarkable tumor regression was observed at both the irradiated focus and distant metastatic sites 2 months later after combined treatment. The patient has tumor mutational burden (8.7 somatic mutations/Mb) and positive PD-L1 expression. The increased circulating lymphocytes suggest induced activation of immune response after combination treatment. Free disease progression has reached one and a half years as far.