PMID- 24756215 OWN - NLM STAT- MEDLINE DCOM- 20140729 LR - 20211021 IS - 1432-2307 (Electronic) IS - 0945-6317 (Linking) VI - 464 IP - 6 DP - 2014 Jun TI - Absence of estrogen receptor alpha (ESR1) gene amplification in a series of breast cancers in Taiwan. PG - 689-99 LID - 10.1007/s00428-014-1576-8 [doi] AB - Immunohistochemical expression of ERalpha, encoded by the ESR1 (estrogen receptor 1) gene located at 6q25.1, is the most important determinant of responsiveness to endocrine therapy in breast cancer. The prevalence and significance of ESR1 amplification in breast cancer remain controversial. We set out to assess ESR1 status and its relevance in breast cancer in Taiwan. We tested tissue samples from 311 invasive carcinomas in a tissue microarray for ESR1 status by fluorescent in situ hybridization (FISH) and chromogenic in situ hybridization (CISH). In order to examine its association with ERalpha and ESR1 status, HER2 status was determined by FISH. Of the carcinomas, 58.8 % (183/311) was ERalpha positive. None of the carcinomas showed amplification of ESR1 by either method, whereas 24.1 % (75/311) of the carcinomas harbored HER2 amplification. Of the carcinomas, 9.6 % (26/301) showed ESR1 gain (1.3