FOXA2 mRNA expression is associated with relapse in patients with Triple-Negative/Basal-like breast carcinoma

The FOXA family of transcription factors regulates chromatin structure and gene expression especially during embryonic development. In normal breast tissue FOXA1 acts throughout mammary development; whereas in breast carcinoma its expression promotes luminal phenotype and correlates with good prognosis. However, the role of FOXA2 has not been previously studied in breast cancer. Our purpose was to analyze the expression of FOXA2 in breast cancer cells, to explore its role in breast cancer stem cells, and to correlate its mRNA expression with clinicopathological features and outcome in a series of patients diagnosed with breast carcinoma. We analyzed FOXA2 mRNA expression in a retrospective cohort of 230 breast cancer patients and in cell lines. We also knocked down FOXA2 mRNA expression by siRNA to determine the impact on cell proliferation and mammospheres formation using a cancer stem cells culture assay. In vitro studies demonstrated higher FOXA2 mRNA expression in Triple-Negative/Basal-like cells. Further, when it was knocked down, cells decreased proliferation and its capability of forming mammospheres. Similarly, FOXA2 mRNA expression was detected in 10% (23/230) of the tumors, especially in Triple-Negative/Basal-like phenotype (p < 0.001, Fisher's test). Patients whose tumors expressed FOXA2 had increased relapses (59 vs. 79%, p = 0.024, log-rank test) that revealed an independent prognostic value (HR = 3.29, C.I.95% = 1.45-7.45, p = 0.004, Cox regression). Our results suggest that FOXA2 promotes cell proliferation, maintains cancer stem cells, favors the development of Triple-Negative/Basal-like tumors, and is associated with increase relapses.