COL1A1 and breast cancer: Our study identified miR-218 as a miRNA associated with breast cancer bone metastasis, which can inhibit the deposition of type I collagen through two mechanisms (Fig. 5e): (1) miR-218 secretion into the EVs and transfer to osteoblasts during differentiation, where miR-218 directly downregulates COL1A1 expression; (2) direct targeting of YY1 in cancer cells to induce inhibin βA expression and secretion, which then represses procollagen processing by inducing TIMP3, an inhibitor of the N-procollagenase ADAMTS2.