These serum markers still lack the adequate sensitivity (below 25%) and specificity (below 70%) to be applicable in diagnosing early stage breast carcinoma in a large population.16,17 Estrogen receptor (ER) and progesterone receptor (PR) facilitate decisions on therapy, but are weak prognostic measures.10,16,18 HER2 over-expression is associated with poor prognosis, but HER2-based mechanisms underlie only about one third of breast cancers. Here, ESR1 is linked to breast cancer.