Purpose: The microenvironment of metastatic breast cancer is incompletely characterized, despite prior evidence that it plays a key role in the biology of metastasis. A major component of the tumor stroma is the carcinoma-associated fibroblast (CAF), which has been shown to communicate with other stromal and cancer cells to create a protumorigenic milieu. Our study was designed to characterize human CAFs from different metastatic sites. Experimental Design: We collected eight carcinoma-associated fibroblasts (mCAFs) from different metastatic sites and compared them with CAFs from primary tumors (pCAFs) and with normal breast fibroblasts (NFs). Molecular profiles and effects on breast cancer cell growth, on response to doxorubicin and on T-cell proliferation were compared.Results: We observed marked differences in mCAFs compared with pCAFs and NFs with respect to proliferation and effects on breast cancer cell migration, spheroid growth, invasion, response to doxorubicin, and tumor growth. We found marked transcriptomic differences between mCAFs and pCAFs, including increased expression of IFN-related genes and IGF2 in the former. Cluster analysis revealed two groups of mCAFs, with the liver mCAFs clustering together, with increased expression. Treatment with an antibody against insulin-like growth factors (BI836845) inhibited growth of mixed mCAF-tumor cell xenografts . Also, mCAFs had a suppressive effect on T-cell proliferation.Conclusions: This is the first comparative analysis of a set of CAFs from metastatic sites in breast cancer. It revealed a marked protumorigenic effect in these mCAFs, which occurs in part through increased expression of IGF2.