318 Skin rash composition after checkpoint inhibitor therapy varies by therapeutic regimen

Cancer patients treated with immune checkpoint inhibitors can experience adverse events affecting different organ systems. Among immune related adverse events, skin rash develops relatively early and might serve as a biomarker of downstream responses to therapy. We questioned whether the cellular composition of skin rash might vary according to the type of treatment applied, to interfere with PD1 signaling alone or combined with CTLA-4 blockade. Skin samples were obtained from consenting adults to perform mono-and multiplex OPAL immunostaining and Vectra imaging of snap frozen or paraffin-embedded rash (n=9) and control (n=8) skin samples.