TGF-β promotes breast cancer cell outgrowth from dormancy in metastatic sites, and our PDX models implicate TGF-β signaling activation in metastasis-initiating cells [20, 66], suggesting that combination therapy of doxorubicin and PFD may have additional inhibitory effects on metastasis-initiating cells. This evidence concerns the gene TGFB1 and breast carcinoma.