Purpose: This study investigated the functional and clinical significance of integrin avb6 upregulation in myoepithelial cells of ductal carcinoma in situ (DCIS).Experimental Design: Archival samples of DCIS and DCIS with associated invasion (n ¼ 532) were analyzed for expression of avb6 by immunohistochemistry and ability to predict recurrence and progression assessedinanindependent,uniquecohortofDCIScaseswithlong-termfollow-up.Primarymyoepithelialcells and myoepithelial cell lines, with and without avb6 expression, were used to measure the effect of avb6 on growth and invasion of tumor cell lines in vitro and in a xenograft mouse model. Involvement of TGFb signaling was established using mink lung epithelial cell (MLEC) assay and antibody inhibition, and expression and activation of matrix metalloproteinase (MMP)-9 established by Real Time-PCR and zymography.Results: Expression of avb6 is significantly associated with progression to invasive cancer (P < 0.006) and with recurrence over a median follow-up of 114 months in a series of matched DCIS cases treated with local excision. We show that expression of avb6 drives myoepithelial cells to promote tumor cell invasion in vitro and enhances mammary tumor growth in vivo. The tumor-promoting effect of avb6-positive myoepithelial cells is dependent on TGFb-driven upregulation of MMP9 and can be abrogated by inhibiting this pathway.Conclusion: These findings indicate that altered myoepithelial cells in DCIS predict disease progression and recurrence and show that upregulation of avb6 on myoepithelial cells generates a tumor promoter function through TGFb upregulation of MMP-9. These data suggest that expression of avb6 may be used to stratify patients with DCIS. Clin Cancer Res; 20(2); 344-57. Ó2013 AACR.

Highlights d Low mural-b3-integrin in tumor BVs is associated with poor prognosis in human cancers d Mural-b3-integrin loss enhances tumor growth in tumor models without vascular changes d Mural-b3-integrin loss upregulates FAK-p-HGFR-p-Akt-p-p65-driven cytokine production d Mural cell-derived CCL2 activates MEK1-ROCK2-dependent tumor growth