For example, primary tumor-derived TGF-β induces the expression and secretion of POSTN by stromal fibroblasts (α-SMA+VIM+) in the pre-metastatic lung of the MMTV-PyMT breast cancer mouse model, sustaining infiltrating metastasis-initiating cells by promoting WNT signaling (151). The gene discussed is TGFB1; the disease is breast carcinoma.