In the absence of distinct hormone content, pituitary transcription factors may be useful to distinguish the differentiation of tumor cells; pituitary specific transcription factor 1 (Pit-1), t-box transcription factor (Tpit), steroidogenic factor (SF-1), estrogen receptor alpha (ER-a), and GATA binding protein 2 (GATA-2) can be employed. The gene discussed is ESR1; the disease is neoplasm.