FNDC5 and cancer: Jiang et al. found in their study on the expression and prognostic analysis of the fibronectin type III domain protein family in human cancer [4] that the mRNA expression levels of FNDC1, FNDC3A, and FNDC3B were significantly higher in most malignant tumors than in nearby normal tissues, while the expression levels of FNDC4, FNDC5, FNDC6, and FNDC8 were significantly reduced.