In the current study we have shown that a subset of breast CAFs (5 of 23 tested CAFs) strongly expresses a type one interferon response and that this response, chiefly through the IFN-β cytokine, can impart a pro-proliferative effect on MCF-7 breast cancer cells in vitro. It should be noted that direct fibroblast-breast cancer cell line contact was necessary when the interferon response was previously induced artificially in vitro [13]. Here, IFNB1 is linked to breast cancer.