On-premises of immuno-histochemical articulation of receptors, specifically estrogen receptor (ER), progesterone receptor (PR), human epidermal development receptor 2 (HER2), breast cancer can be partitioned into four significant subcategories, ER+/PR+/HER2−, ER+/PR+/HER2+, ER−/PR−/HER2+, and ER−/PR−/HER2−. The gene discussed is ESR1; the disease is breast cancer.