SFRP1 and breast cancer: Though SFRP1 expression has been found to be reduced in both human primary tumours as well as breast cancer cell lines relative to normal primary human mammary epithelial cells [37], we have not been able to detect Sfrp1 mRNA in cancerous or normal canine mammary epithelial cell lines by RT-qPCR, but it was strongly expressed in a canine fibroblast cell line (data not shown).