Given that TGF-β/Smad signaling is implicated in breast cancer metastasis31 and miR-18a has been demonstrated to directly regulate Smad2 in neuroblastoma cells28, we hypothesized that miR-18a-mediated regulation of Smad2 expression is involved in the suppressive effect of Rd treatment on breast cancer metastasis. Here, SMAD2 is linked to breast carcinoma.