Pathophysiologies of cancer-associated syndromes such as cachexia are poorly understood and no routine biomarkers have been established, yet. Using shotgun proteomics, known marker molecules including PMEL, CRP, SAA, and CSPG4 were found deregulated in patients with metastatic melanoma. Targeted analysis of 58 selected proteins with multiple reaction monitoring was applied for independent data verification. In three patients, two of which suffered from cachexia, a tissue damage signature was determined, consisting of nine proteins, PLTP, CD14, TIMP1, S10A8, S10A9, GP1BA, PTPRJ, CD44, and C4A, as well as increased levels of glycine and asparagine, and decreased levels of polyunsaturated phosphatidylcholine concentrations, as determined by targeted metabolomics. Remarkably, these molecules are known to be involved in key processes of cancer cachexia. Based on these results, we propose a model how metastatic melanoma may lead to reprogramming of organ functions via formation of platelet activating factors from long-chain polyunsaturated phosphatidylcholines under oxidative conditions and via systemic induction of intracellular calcium mobilization. Calcium mobilization in platelets was demonstrated to alter levels of several of these marker molecules. Additionally, platelets from melanoma patients proved to be in a rather exhausted state, and platelet-derived eicosanoids implicated in tumor growth were found massively increased in blood from three melanoma patients. Platelets were thus identified Serum is the most important diagnostic sample type because of its minimal invasive access, a relatively high stability and its comprehensive representation of the physiological state of an individual. The latest technological development of mass spectrometric instruments, such as high resolution orbitrap instruments, improved substantially the quality and reliability of serum proteomics data (1). Shotgun proteomics analysis using the orbitrap technology is mainly applied for protein screening purposes (2). This method allows performing untargeted analyses, applicable for hypothesis-generating clinical applications. Targeted proteomics using triple-quadrupole mass spectrometric instruments, represents a complementary approach which is applied for protein quantification, hypotheses verification and validation (3). Enormous efforts have been invested in the last decades focusing on serum biomarker discovery (4). However, mass spectrometrybased proteomics analyses hardly managed to cope with biological variation. As a consequence, almost no clinically validated biomarker has emerged from these investigations yet, and a lot of questions about pathophysiological mechanisms remain unanswered.Using mass spectrometry-based proteomics, we have previously investigated melanoma and neighboring stroma cells, focusing on the identification of biomarkers associated with intrinsic and extrinsic drug resistance (5). In the present article, we followed the question how metastatic melanoma may reprogram distant organ functions, and how these...