FNDC5 and breast carcinoma: The serum irisin levels were significantly lower in patients with colon, bladder, liver, and breast cancers than in healthy controls (Provatopoulou et al., 2015; Pazgan-Simon et al., 2020; Taken et al., 2022; Celik et al., 2023), whereas they were elevated in patients with kidney cancer (Altay et al., 2018).