Low dose pembrolizumab in the treatment of advanced non-small cell lung cancer.

A dose of 200mg 3-weekly of pembrolizumab was approved by the FDA as treatment for advanced NSCLC without oncogenic drivers. This is despite evidence showing no difference in efficacy with 2mg/kg. This study aimed to assess the efficacy of a lower fixed dose of 100mg, which is closer to 2mg/kg weight-based dose in an average sized Asian patient. All patients receiving pembrolizumab for advanced NSCLC from January 2016 to March 2020 in National University Hospital, Singapore, were included in this retrospective observational study. The effect of pembrolizumab 100mg (Pem100) versus 200mg (Pem200) upon survival outcomes, toxicity and cost were examined. 114 patients received pembrolizumab. 65 (57%) and 49 (43%) received Pem100 and Pem200 respectively. There was no difference in progression-free survival (PFS) and overall survival (OS) between Pem100 vs Pem200 as a single agent (PFS: 6.8 vs 4.2months, HR 0.72, 95%CI 0.36-1.46, p=0.36; 9 month OS: 58% vs 63%, HR 1.08, 95%CI 0.48-2.41, p=0.86) and when combined with chemotherapy (9-month PFS: 60% vs 50%, HR0.84, 95%CI0.34-2.08, p=0.71; 9-month OS: 85% vs 58%, HR 0.27, 95%CI 0.062-1.20, p=0.09). No significant difference in response rate or ≥G3 immune-related toxicities between Pem100 and Pem200 was observed. A cost minimisation analysis evaluating the degree of cost savings related to drug costs estimated a within study cost saving of SGD4,290,912 and cost saving per patient of SGD39,942 in the Pem100 group. 100mg of pembrolizumab appears to be effective with reduction in cost. A randomised trial should be done to investigate a lower dose of pembrolizumab.