FOXA1 is an independent prognostic marker for ER-positive breast cancer

Forkhead box protein A1 (FOXA1) is a "pioneer factor" that plays a role in controlling nearly 50% of estrogen receptor target genes. FOXA1 expression correlates with estrogen receptor (ER)-positivity especially in luminal subtype A breast cancers. The aim of this study was to investigate the precise role of FOXA1 in breast cancer using a large population-based cohort. Nuclear expression of FOXA1 was analyzed in a tissue microarray of 4,444 invasive breast cancer cases using immunohistochemistry and correlated with clinicopathologic variables using previously described methods and cutoff points. The entire cohort was equally divided into a training and validation set. All survival analyses were performed using a previously defined cutoff (3) for validation. Additional X-tile analysis performed to analyze prognostic effects of low and high FOXA1 levels identified 24 as a cutoff. Bonferroni-Holmes test was used as appropriate. FOXA1 expression significantly correlated positively with markers of good prognosis or ER-positivity, and negatively with tumor size, tumor grade, nodal status, Ki67, HER2 expression, and basal subtype (each P value