Cancer cachexia is defined by an ongoing loss of skeletal muscle mass.

Since 2007, a quantitative, specific and precise approach to the detection of muscle loss has become accessible with the advent of image-based assessments. Computed tomography images acquired as part of standard cancer care are the serendipitous substrate for these analyses. Three radiologically-determined abnormalities, sarcopenia (severe muscle depletion), catabolic loss of muscle over time, and reduced muscle radiation attenuation associate with progressive functional impairment, treatment-related complications, reduced quality of life, and mortality. Fundamental understanding of muscle wasting in cancer cachexia has been developed on a base of clinical and experimental studies, which have identified alterations in muscle protein synthesis, autophagy and ubiquitin-mediated proteolysis as key contributors to muscle loss. The etiology of cancer-associated muscle wasting is multifactorial. Tumor metabolism captures energy fuels and amino acids, and a suite of tumor-derived molecules elicits catabolic pathways at the tissue level in muscle. Endocrine, neural and inflammatory derangements add further catabolic drive. Antineoplastic agents make a substantial contribution to muscle wasting by directly action on muscle cells, as well as secondarily via their systemic side effects. Encouraging data is emerging as to the potential reversibility of muscle loss and/or reduced muscle radiation attenuation through modulation of specific mechanisms. In the first line, pain and symptom management is a key element of the prevention of catabolic loss of muscle. Intake of intake of high-quality proteins and ω-3 polyunsaturated fatty acids support retention or gain of muscle mass. While there is no approved drug therapy for the indication of cancer-associated muscle wasting, there is preliminary evidence for robust gain of skeletal muscle mass in research studies of new therapeutics including inhibitors of mitogen-activated protein kinase kinases and ghrelin receptor agonists.