Clinical Characteristics and Pharmacokinetics Change of Long-Term Responders to Antiprogrammed Cell Death Protein 1 Inhibitor Among Patients With Advanced NSCLC.

Introduction: Immune checkpoint inhibitors (ICIs) induce long-term, durable responses in patients with advanced NSCLC. Nevertheless, these responses are limited to a few patients, and most responders have disease progression. The purpose of this study was to determine the differences in clinical factors and blood drug concentrations between long-term responders (LTRs) and non-LTRs. Methods: We retrospectively analyzed consecutive patients with advanced NSCLC who received antiprogrammed cell death protein 1 (PD-1) inhibitor monotherapy (nivolumab) from December 22, 2015, to May 31, 2017. Patients who obtained a clinical benefit for more than 6 months were referred to as "responders"; among these, individuals who had a durable response for more than 2 years were defined as "LTRs." Those with a clinical benefit for less than 2 years were defined as "non-LTRs." Results: A total of 212 patients received anti-PD-1 inhibitor monotherapy. The responders accounted for 35% (75 of 212) of the patients. Of these, 29 (39%) were LTRs and 46 (61%) were non-LTRs. The overall response rate and median tumor shrinkage in the LTR group were significantly higher than those in the non-LTR group (76% versus 35%, p < 0.0001, and 66% versus 16%, p < 0.001, respectively). The groups had no significant difference in PD-L1 expression and serum drug concentration at 3- and 6-month post-treatment initiation. Conclusions: Significant tumor shrinkage was associated with a long-term response to an anti-PD-1 inhibitor. Nevertheless, the PD-L1 expression level and pharmacokinetic profile of the inhibitor could not be used to predict the durable response among the responders.