Emerging significance of estrogen cancer coregulator signaling in breast cancer.

Estrogen receptor (ERα) plays an important role in the initiation and progression of breast cancer. Many breast cancer patients respond positively to hormonal therapy; however, initial or acquired resistance to endocrine therapies frequently occurs and tumors recur as metastases. Emerging evidence suggests that ERα action is complex and involves functional interactions with coregulators. The levels of ERα coregulator proteins are tightly regulated under normal conditions and ERα-coregulator proteins have the potential to be differentially expressed in malignant tumors and have altered functions leading to tumor progression and metastases. In this review, we summarize recent findings that relate to ERα coregulators and discuss implications of ERα coregulator deregulation in breast cancer metastasis.