GDF15 and cancer: The association of circulating GDF‐15 levels with muscle mass is not unique to COPD as GDF‐15 has been associated with cancer cachexia36 in a number of studies, and we have shown that patients who show wasting of the rectus femoris following cardiac surgery are exposed to a more sustained elevation of GDF‐15 than those who do not waste.11 Furthermore, the link between GDF‐15 and all‐cause mortality may reflect the effects of this growth factor on muscle homeostasis.