Skeletal muscle adaptations to cancer and its treatment: their fundamental basis and contribution to functional disability

Cancer is a physically disabling condition. Functional disability, defined as an inability or impaired ability to perform simple tasks of daily life, afflicts a large majority of the cancer population and dramatically impacts patient well-being, negatively affecting treatment decisions, quality of life, and clinical outcomes. Our current understanding of the fundamental mechanisms underlying physical disability in cancer patients, however, is limited. This review will evaluate how cancer and cancer treatments and their pathological sequelae alter skeletal muscle structure and function to promote functional disability. Briefly, factors associated with cancer and its treatment can diminish skeletal muscle size and contractile function, which lead to a reduced physiological capacity for work and, in turn, functional disability. We outline the clinical evidence for the involvement of each of these factors in disability in cancer patients and then review structural and functional evidence at various anatomic levels to explore the tissue, cellular, and molecular mechanisms underlying cancer-related disability.