Immunohistochemical validation of multiple phospho-specific epitopes for estrogen receptor α (ERα) in tissue microarrays of ERα positive human breast carcinomas

Estrogen receptor a (ER alpha) activity is regulated by phosphorylation at several sites. Recently several antibodies specific for individual phosphorylated sites within ERa have became available. Such antibodies potentially provide invaluable tools to gain insight into the relevance in vivo of phosphorylated ERa in human breast tumors. However, validation of these antibodies for immunohistochemistry in particular is necessary in the first instance. In this study we have investigated the usefulness of several antibodies generated to specific phosphorylated sites within ERa for immunohistochemistry of formalin-fixed, paraffin-embedded human breast cancer biopsy samples. As well, these data demonstrate for the first time, the detection of multiple phosphorylated ERa forms in breast cancer (P-S104/106-ER alpha, P-S118-ER alpha, P-S167-ER alpha, P-S282-ER alpha, P-S294-ER alpha, P-T311-ER alpha, and P-S559-ER alpha) suggesting the possibility that profiling of phosphorylated ERa isoforms might be useful in selecting subgroups of breast cancer patients that would benefit from endocrine therapy.