ESR1 and neoplasm: Earlier radiometric assays measured ER levels by the direct binding of [3H]estradiol, ex vivo on extracts of fresh or frozen tumor samples; current ER IHC assays measure an antigenic signal from ER on formalin-fixed, paraffin -imbedded (FFPE) sections from fine-needle biopsies and are graded on scales that consider staining intensity and distribution of stained cells [135,136].