FNDC5 and breast cancer: For example, increased levels of irisin were found in liver- and renal-cancer patients (Gaggini et al., 2017; Altay et al., 2018), while decreased levels were detected in colorectal- and breast-cancer patients (Provatopoulou et al., 2015; Zhang et al., 2018; Zhu et al., 2018; Figure 4).