ESR1 and ductal breast carcinoma in situ: Furthermore, since coincident ER-negativity/HER2-positivity in DCIS patients has been associated with larger tumors and increased recurrence rates [33], in addition to cancer stem cell enrichment [34], the subset of DCIS patients represented by SUM-225 cells has greater need of new drug targets than the majority of DCIS patients with low-risk ER-positive disease.