FNDC5 and breast cancer: FNDC5 mRNA expression levels in normal breast cells (Me16c) were significantly lower (mean 1.03 ± 0.05 SD) compared to the levels found in the cells of all BC lines (MCF-7, mean 30.71 ± 8.43 SD, p = 0.0037; MDA-MB-231, mean 7.58 ± 4.05 SD, p = 0.0492; MDA-MB-468, mean 111.60 ± 41.93 SD, p = 0.0103).