Early diagnosis of cancer is key for improving patient outcomes, but cancers are difficult to diagnose if patients present with unspecific symptoms. The principal objective of the MEDECA (Markers in Early Detection of Cancer) study is to identify a multi-analyte blood test that can detect and map occult cancer within a mixed population of patients presenting with serious but unspecific symptoms. The study will include 1500 patients referred to the Diagnostic Center at Danderyd Hospital (DC DS), a multidisciplinary diagnostic center referral pathway for patients with radiological findings suggestive of metastasis without known primary tumor or suspicion of serious but unspecific symptoms. Blood samples are collected prior to a standardized and extensive cancer diagnostic work-up, including an expanded panel of biochemical analyses and extensive imaging such as computed tomography or magnetic resonance investigations. In collaboration with world-leading international scientists, the blood samples will be analyzed for a panel of novel and established blood biomarkers predictive of an underlying cancer, including markers of neutrophil extracellular traps, circulating tumor DNA, platelet mRNA profiling, affinity-based proteomics and nuclear magnetic resonance metabolomics. The diagnostic accuracy of the blood biomarkers with respect to cancer detection during the diagnostic work-up will be analyzed through machine learning.