SFRP1 and breast neoplasm: In parallel, aging fibroblasts display an altered secretome, with secretion of the Wnt antagonists secreted frizzled-related protein (sFRP)1 and sFRP2 promoting metastatic outgrowth17,39, and, similarly, intranasal administration of transforming growth factor (TGF)-β creates a fibrotic environment, supporting outgrowth of breast tumor cells in the lungs4.