Added PubMed ID Background Loss of skeletal muscle mass in cancer cachexia is recognized as an independent predictor of mortality. Mechanisms involved in this wasting process and parameters for early diagnosis are not yet clearly defined. As skeletal muscle is considered as a secretory organ, the aim of this present experimental work was to characterize the changes in the putative muscle secretome associated with cancer-induced cachexia to gain a better understanding of cellular mechanisms involved and to identify secreted proteins which might reflect this wasting process. Methods We investigated first the changes in the muscle proteome associated with cancer-induced cachexia by using differential label-free proteomic analysis on muscle of the C26 mouse model. The differentially abundant proteins were then submitted to sequential bioinformatic secretomic analysis in order to identify potentially secreted proteins. Multiple reaction monitoring and Western blotting were used to verify the presence of candidate proteins at the circulating level. Finally, we investigated the regulation of the production of these secreted proteins by muscle in vitro and in vivo. Results Our results revealed a dramatic increased muscular production (2-to 25-fold) of several acute phase reactants (APR: haptoglobin, serpina3n, complement C3, serum amyloid A1) which are released in the circulation during C26 cancer cachexia. This observation was confirmed in two other preclinical models of cancer cachexia as well as in cancer patients. The muscular origin of these APR was demonstrated by their increased expression in skeletal muscle and myotubes. Our results showed also that IL-6 plays a major role in the muscular induction of these APR in vivo, while glucocorticoids and pro-inflammatory cytokines stimulate directly their increased expression in muscle cells in vitro. Conclusions Muscle wasting caused by cancer is associated with marked changes in muscle secretome. Our study demonstrates a marked increased production of APR by skeletal muscle in pre-clinical models of cancer cachexia and in cancer patients. Further studies are required to unravel the potential role of these proteins in muscle atrophy and their interest as biomarkers of cancer cachexia.