ESR1 and inflammatory breast carcinoma: In the routine diagnosis of IBC, surrogate markers are used by immunohistochemistry (IHC), such as estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), and  the Ki67 proliferation index, as tools to estimate the risk of micrometastasis and relapse, as well as to stratify for treatment [12].