The estrogen receptor test (ERT) uses the estrogen receptor (ER) tumor marker that allows for immunohistochemical techniques to be performed for diagnostic purposes. Immunohistochemistry (IHC) techniques involve the selective identification of antigen proteins by exploiting these antigen-antibody relationships to characterize your analyte of interest. Previously, the ligand binding assay has been used in the determination of ER activity, however, this method was limited because of the requirement of large quantities of fresh tissue needed for each assay. IHC serves as a more efficient method as this technique allows for the morphology of the tissue to be observed in a tumor-specific manner. This increases the practicability of this technique as in many cases, patients’ tissue samples are limited in the applications of biomarker analysis. Anti-estrogen receptor antibodies were among the first of biomarkers that introduced a semi-quantitative assessment of the ER activity. Today, ER analysis is one of many routinely performed immunohistochemical assays performed to classify the hormone receptor status and to serve as a means of insight into the determination of cancer prognosis and management. Estrogen receptor test The ER activity can be monitored using immunohistochemical methods in applications like tissue analysis for tumorigenesis. The activation of the ER through binding to the estrogen hormone stimulates the mammary cell division, catalyzing the cell division and DNA replication process. This results in exponential multiplication of replications of the mutated genes, along with large amounts of genotoxic waste in response to this estrogen metabolism pathway. These ill effects highly increase the chances of malignant cell formation, and in turn, increase the chance of tumor formation. Estrogen receptor types There are two main types of estrogen receptors: estrogen receptor alpha (ERα) also known as NR3B1, and estrogen receptor beta (ER-β) also known as NR3A2. Both of these are nuclear receptors activated by the sex hormone, estrogen, and encoded by the ESR1 (Estrogen Receptor 1) gene. The estrogen signaling can be stimulated or inhibited selectively. This is dependent upon the equilibrium of these 2 receptor types in target organs. These two ER types are encoded by different genes located on separate chromosomes and have different functions. ERα is mostly active in the mammary gland and uterus, and aids in the regulation of skeletal homeostasis and metabolism. ER-β on the other hand, plays a more prominent role in the central nervous and immune systems functional mechanisms. Immunohistochemical assessment The ERT immunohistochemical assessment is a semi-quantitative