IGF1 and chronic obstructive pulmonary disease: Whereas the levels of several classical cytokines associated with muscle wasting (such as TNF-a, insulin-like growth factor-1, hypoxia inducible factor 1, and mammalian target of rapamycin) are increased in COPD, the role of TWEAK in muscle mass loss during COPD remains unknown [1, 4, 7, 8].