Estrogen receptor expression in human tumors: A tissue microarray study evaluating more than 18,000 tumors from 149 different entities.

Estrogen receptor (ER) is a ligand-activated transcription factor with a critical role in development and function of multiple organ systems and a well-established drug target for breast cancer. To comprehensively evaluate ER expression in normal and tumor tissues, a tissue microarray containing 18,560 samples from 149 different tumor types and subtypes and 608 samples of 76 different normal tissue types was analyzed by immunohistochemistry (IHC). ER positivity was found in 55 different tumor types including 26 entities with at least one strongly positive tumor.