IGFBP4 and renal cell carcinoma: Additionally, the aberrant Wnts signaling in RCC was also caused by the loss of function of Wnt antagonists, for example by the downregulation of WIF1 (Wnt inhibitory factor 1), members of sFRP (secreted frizzled-related protein) family, Dkk (Dickkopf) family, IGFBP4 (insulin-like growth factor-binding protein 4) and SOSTDC1 (sclerostin domain-containing protein 1) [62,63,64,65].