Both transdermal 4-hydroxytamoxifen and telapristone acetate have been evaluated in neo-adjuvant phase II studies enrolling patients with estrogen receptor positive ductal carcinoma in situ (DCIS)29or in patients with or without localized breast cancer scheduled for mastectomy30, respectively, and randomized against patients receiving comparable systemic therapy. Here, ESR1 is linked to ductal breast carcinoma in situ.