ESR1 and ductal breast carcinoma in situ: Table 1 provides an overview of the clinicopathological data of all patients. The overall median age was 53 years (range 28–102 years). The majority of DCIS and IBC samples were high grade (62.3 and 54.7%, respectively). There was no difference in grade between DCIS and adjacent IBC (Fisher Exact Probability Test p = 0.92). Based on immunohistochemical staining, IBCs were categorized into the following five breast cancer subtype categories: ER+/PR high/Her2− (n = 13), ER+/PR− or low/Her2− (n = 12), ER+/any PR/Her2+ (n = 11), ER−/PR−/Her2+ (n = 8), or ER−/PR−/Her2− (n = 9).