SFRP1 and cancer: In particular, activation of Wnt pathway by suppression of Wnt antagonists, namely SFRP1, SFRP2, SFRP5, and WIF-1 appears to play a very prominent role in the proliferation of many RCC cell lines and patient tumor samples—as determined by a higher percentage of methylation in cancer tissue compared to normal tissue, very low expression compared to normal tissue, significant inhibition of proliferation, and increase in apoptosis caused by transfection of the Wnt antagonist genes.