e23019 Background: Ductal carcinoma in situ (DCIS) is a well-known precursor of invasive ductal carcinoma (IDC). Part of patients show disease recurrence as DCIS or IDC after local treatment, but there are no established markers for prediction of recurrence. Methods: Authors analyzed 30 patients diagnosed as pure DCIS, recurrent DCIS, and IDC progressed in DCIS background. miRNA was extracted from archival tissue, and hierarchical clustering of miRNA microarray was performed. We selected highly expressed miR-17-5p and miR-106b-5p as marker for recurrence of DCIS. Two miRNAs were transfected to MCF-12 and MCF-7 cell line. Cell proliferation assay and Western blot analysis was performed for analyzing the interaction between cell proliferation and TGFβ downstream pathway. Results: miR-106b-5p single and combined miR-106b-5p and miR-17-5p transfected MCF-12 cell line showed increased proliferation index compared to un-transfected cell line. In MCF-7, miR-106b and miR-17-5p transfected cell line showed inferior proliferation index compared to un-transfected cell line. Western blot analysis showed minimal increased expression of SMAD4, phosphorylated SMAD2 (pSMAD2) in miR-106b-5p and miR-17-5p transfected MCF-12 cell line. However, decreased expression of TGFBR2 and no interval change of SMAD4 and pSMAD2 was detected in miR-106b-5p and miR-17-5p transfected MCF-7 cell line. Conclusions: miR-106-5p, miR-17-5p showed increased expression in recurrent DCIS or IDC based on miRNA hierarchical microarray. miRNA transfected MCF-12 cell line showed increased proliferation index and activated TGFβ downstream pathway. miRNA transfection might have made normal cell line to pre-cancerous cell line and TGFβ pathway might have influenced to promote tumor proliferation, based on TGFβ paradox hypothesis.