Despite increasing interest in biomarkers to diagnose and distinguish diseases and select treatment few new protein biomarkers are being successfully validated. Important explanations for the limited success are poor specificity and sensitivity of detection of plasma proteins using current assays, and inability to analyze large numbers of markers and samples. Improved assays should provide access to plasma protein biomarkers at levels below current detection thresholds, potentially reflecting disease processes anywhere in the body at early stages. They should also distinguish closely similar protein variants. The assays should furthermore assess numerous markers in parallel with limited consumption of biobank samples.The aim of this project is to enable investigations of protein biomarkers at entirely new levels of performance. The basis of the proposal is our expertise in molecular tools and specifically an approach to protein analysis that addresses the above requirements.This technology is now ready to be scaled for large-volume, high-performance assays with the following characteristics: 1) Unsurpassed specificity via simultaneous detection of three epitopes on any target protein. 2) Amplifiable DNA strands form upon specific detection, permitting ultrasensitive detection. 3) Only appropriate reagent combinations result in amplifiable reporter strands, overcoming obstacles to multiplex protein detection. 4) Tag sequences in the amplified DNA strands identify the detected proteins and the investigated samples, allowing digital information of protein abundance to be retrieved via next generation DNA sequencing of multiplex reactions for large numbers of patients in single runs.I propose to set up and apply assays of a thousand proteins in parallel in small plasma samples, and in a subproject I will target proteins on a novel and promising class of cancer biomarkers – exosomes.