For the case–case study we defined the following tumor subtypes: ER+ (852 cases) vs. ER− (190 cases); PR+ (709 cases) vs. PR− (333 cases); ER+/PR+ (703 cases) vs. ER−/PR− (184 cases); ER+/PR− (149 cases) vs. ER−/PR− (184 cases) and HER2+ (123 cases) vs. HER2− (949 cases) (Table 1). Here, ESR1 is linked to neoplasm.