ESR1 and ductal breast carcinoma in situ: In a randomized trial (TAM-01) comparing low-dose tamoxifen (5 mg/day for 3 years) with observation alone for preventing local recurrence in women who had hormone receptor-positive (ER or progesterone receptor ≥ 1%) intraepithelial neoplasia (including atypical ductal hyperplasia and lobular or ductal carcinoma in situ) after BCS, DeCensi et al. showed a significant decrease in ipsilateral and contralateral recurrent events in patients who received low-dose tamoxifen than those without, in which RT was preserved for patients with high-risk factors of DCIS [13].