MMP9 and ductal breast carcinoma in situ: Presence of integrin β6 on myoepithelial cells has been shown to be correlated with the progression from ductal carcinoma in situ (DCIS) to invasive ductal carcinoma (IDC) by generating a tumor promoter function through up‐regulation of matrix metallo‐protease 9 (MMP9) 8, 9.