Cancer cachexia is defined as a multifactorial syndrome characterized by an ongoing loss of skeletal muscle mass with or without loss of fat mass. The syndrome cannot be fully reversed by conventional nutritional support, and despite an increased number of studies related to cancer cachexia, the underlying mechanisms are still poorly defined, and therapeutic options are limited. This review focuses on recent studies investigating mechanisms and pathways in cancer cachexia. The role of molecular and functional imaging in identifying cachexia at an earlier stage, in identifying potential metabolic targets and pathways, and in assessing treatment efficacy is also reviewed.