ESR1 and ductal breast carcinoma in situ: A national audit of DCIS in the UK revealed that ER status was assessed in only 50 % of DCIS cases and ER positivity in low and intermediate grade DCIS was significantly more common than in high grade DCIS (P <0.001) (ER+ high grade 69 %, intermediate grade 94 %, low grade 99 %) [27].