Four molecular subtypes have been identified in tumor tissue based on the degree of expression of human epidermal growth factor 2 (HER2) and hormone receptors (HR, including estrogen receptors [ER] and progesterone receptors [PR]): HER2−/HR+, HER2+/HR+, HER2+/HR− and HER2−/HR− (also referred to as triple-negative) [4]. Here, ESR1 is linked to neoplasm.