NCOA3 is a transcriptional coactivator protein that contains several nuclear receptor interacting domains and an intrinsic histone acetyltransferase activity.

[7][8] The ratio of PAX2 to AIB-1 protein expression may be predictive of the effectiveness of tamoxifen in breast cancer treatment.

[12] In both conditions, the equilibrium of estrogen receptor (ER) complex formation is displaced towards a transcriptionally active complex and thus, counteracting the inhibition caused by anti-estrogenic drugs such as tamoxifen or fulvestrant (selective estrogen receptor modulators).

Notably, tumors diagnosed with concomitant overexpression of AIB1 and HER2/neu have worse outcome with tamoxifen therapy than all other patients combined.

[13] In addition, dormant tumor cells of luminal breast cancers treated with endocrine therapy may acquire with time, mutations that alter kinase signalling pathways and ultimately enhance AIB1 oncogenic functions.