FOXA1 (forkhead box A1, hepatocyte neuclear factor 3a, HNF3A) is a forkhead box domain transcription factor and nuclear steroid receptor involved in mediating sex hormone-dependent signaling in the differentiation and development of tissues such as the pancreas, liver, breast and prostate. Expression of FOXA1 has been associated with a good prognosis in hormone receptor positive breast cancer. It is a useful marker for luminal A type breast cancers, as it is often expressed in luminal subtypes independent of ER expression and it does not see expression in basal subtypes. In ER-negative tumors, a lack of FOXA1 expression is associated with worse prognosis, as loss of FOXA1 is associated with the consequential expression of metastases-prone, basal-specific proteins that it normally acts to directly repress. FOXA1 is expected to show nuclear expression in tissues such as prostate, breast, urothelium, the GI tract and respiratory epithelium. References: EMBO J. 2011 30(19):3885; Bernardo, 2013; Algergaria, 2001; Gong, 2014; Expert Rev Mol Med 2009 5(11):e8; Breast Cancer Res 2009 11(3):R40; Mol Endocrinol 2010 24(8):1594; Ann Surg Oncol 2012 19(4):1145