SFRP2 and breast cancer: In the course of this work, secreted frizzled-related protein 2 (sFRP2) was identified as a TGF-β1–upregulated gene in fibroblasts in vivo that directly drives AEC2s toward BC metaplasia ex vivo, implicating sFRP2 as a strong mediator of pathological fibroblast-AEC2 interaction.