Programmed cell death 1 (PD-1) targeting in patients with advanced osteosarcomas: results from the PEMBROSARC study.

There are some lines of evidence suggesting a potential role of immunotherapy for treating patients with osteosarcomas. This was an open-label, multicentre, phase 2 study of pembrolizumab in combination with metronomic cyclophosphamide in patients with advanced osteosarcomas. All patients received 50 mg b.i.d. of cyclophosphamide one week on and one week off and 200 mg of intravenous pembrolizumab (every 3 weeks). There was a dual primary end-point, encompassing both the non-progression and objective responses at 6 months per Response Evaluation Criteria in Solid Tumours (RECIST), version 1.1. An objective response rate of 20% and/or a 6-month non-progression rate of 60% were determined as reasonable objectives for treatment with meaningful effect. Correlative studies of immune biomarkers were planned from the patients' tumour samples. Between October 13 2015 and July 3 2017, 17 patients were included. Fifty were assessable for the efficacy end-point. Four patients experienced tumour shrinkage, resulting in a partial response (PR) in one patient (6.7%). The 6-month non-progression rate was 13.3% (95% confidence interval [CI]: 1.7-40.5). The most frequent adverse events were grade I or II nausea, anaemia, anorexia and fatigue. programmed death-ligand 1 (PD-L1) expression rate was low, observed in only 2 cases of 14 with available tumour material. The only patient who experienced PR had a PD-L1-negative tumour. Programmed cell death 1 (PD-1) inhibition has limited activity in osteosarcomas. Further studies investigating PD-1 inhibitor in combination with agents modulating the microenvironment are warranted. This study is registered with ClinicalTrials.gov, number NCT02406781.

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