Fig. 1.

Study overview. Twenty-four patients with metastatic melanoma were enrolled in the study at Aarhus University Hospital in 2017. Prior to receiving systemic treatment with first-line checkpoint inhibitors, a baseline blood sample was taken. Subsequently, 10 patients were selected to receive treatment with Pembrolizumab and the remaining 14 patients received a combination of Nivolumab and Ipilimumab. Over the course of treatment, three additional blood samples were extracted. After cell-free DNA extraction from plasma, circulating tumor DNA was sequenced at 15000x depth using a custom gene panel consisting of 40 genes known to be associated with immunotherapy response. Mutations were called in the resulting ctDNA data by running the Shearwater algorithm on a per-sample basis, using the samples from independent patients as background. Following statistical analyses were performed in R.