Amplified in breast cancer 1 (AIB1), also frequently called NCOA3 (nuclear receptor coactivator 3) or SRC3 (steroid receptor coactivator 3), is overexpressed in ~60% of human breast cancers, and increased levels of AIB1 are associated with tamoxifen resistance and decreased overall survival.189 Steroid receptor coactivator 1 (SRC1) is also associated with the chromosomal translocation t(2;2)(q35;p23), which results in PAX3–NCOA1 gene fusion in rhabdomyosarcoma without a consistent genetic abnormality during embryonic development190 (Table 2). Here, NCOA3 is linked to breast cancer.