Relationships between lymphocyte counts and treatment-related toxicities and clinical responses in patients with solid tumors treated with PD-1 checkpoint inhibitors

// Adam Diehl 1 , Mark Yarchoan 2 , Alex Hopkins 2 , Elizabeth Jaffee 2 and Stuart A. Grossman 2 1 Department of Medicine at The Johns Hopkins Hospital, Baltimore, MD, USA 2 The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, MD, USA Correspondence to: Stuart A. Grossman, email: grossman@jhmi.edu Keywords: lymphopenia; PD-1 inhibitor; response; immune-related adverse event; radiation Received: July 27, 2017     Accepted: November 28, 2017     Published: December 14, 2017 ABSTRACT The relationships between absolute lymphocyte counts (ALC), drug- related toxicities, and clinical responses remain unclear in cancer patients treated with PD-1 (programmed cell death 1) inhibitors. We performed a retrospective review of 167 adult solid tumor patients treated with nivolumab or pembrolizumab at a single institution between January 2015 and November 2016. Patients with an ALC >2000 at baseline had an increased risk of irAE (OR 1.996, p 1000 at 3 months (HR 2.76, p<0.05). Prior radiation therapy was the characteristic most strongly associated with lymphopenia at 3 months (OR 2.24, p<0.001). These data suggest that patients with higher baseline lymphocyte counts have a greater risk for irAE, whereas patients with lymphopenia at baseline and persistent lymphopenia while on therapy have a shorter time to progression on these agents. These associations require further validation in additional patient cohorts.