Open AccessESR1 gene status correlates with estrogen receptor protein levels measured by ligand binding assay and immunohistochemistry
Author(s) -
Laenkholm Anne-Vibeke,
Knoop Ann,
Ejlertsen Bent,
Rudbeck Tine,
Jensen Maj-Britt,
Müller Sven,
Lykkesfeldt Anne Elisabeth,
Rasmussen Birgitte Bruun,
Nielsen Kirsten Vang
Publication year - 2012
Publication title -
molecular oncology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.332
H-Index - 88
eISSN - 1878-0261
pISSN - 1574-7891
DOI - 10.1016/j.molonc.2012.04.003
Subject(s) - estrogen receptor , estrogen receptor alpha , immunohistochemistry , biology , estrogen , breast cancer , fluorescence in situ hybridization , gene duplication , cancer research , medicine , endocrinology , cancer , microbiology and biotechnology , gene , immunology , genetics , chromosome
The Estrogen Receptor (ER) is an established predictive marker for the selection of adjuvant endocrine treatment in early breast cancer. During the 1990s Immunohistochemistry (IHC) replaced cytosol based assays for determination of ER status. This study examined the association between ER protein level determined by two different methods and ESR1 gene copy number. From 289 primary high‐risk breast cancer patients, randomized in the Danish Breast Cancer Cooperative Group (DBCG) 77C trial, results from cytosolic ER levels were available from ligand binding assays. Archival tumor tissue was retrieved from 257 patients. ESR1/CEN‐6 ratio was analyzed successfully by Fluorescence In Situ Hybridization (FISH) in 220 (86%) patients. ESR1 amplification (ESR1/CEN‐6 ≥ 2.00) was observed in 23% of the patients and ESR1 deletion (ESR1/CEN‐6 < 0.80) was observed in 32%. Further, we identified ESR1 gain (ratio ESR1/CEN‐6 from 1.30 to 1.99) in 19% of the patients. A positive correlation of ESR1 FISH with both ER‐cytosol and ER IHC was found (p < 0.0001). Amplification and gain of the ESR1 gene are associated with higher ER protein content measured by ligand binding assay and a more intense nuclear staining by IHC compared to tumors with normal ESR1 gene status. Major variations in ER measured by ligand binding assay and IHC are observed within all ESR1 copy number subgroups and other mechanisms than gene copy number seem to contribute to the ER protein content in the tumors.