ESR1 and ductal breast carcinoma in situ: The “intrinsic subtypes” of IBC (97) have been used to categorize DCIS, with an IHC approximation finding DCIS to be 49% Luminal A (ER+, Ki67 low), 8.7% Luminal B/HER2− (ER+, Ki67 high), 17% Luminal B/HER2+ (ER+, HER2+), 16% HER2 (ER−, HER2+), and 7% Triple Negative (ER−, PR−, HER2−) (98).