KLF9 and breast cancer: Additionally, an inverse correlation was found between KLF9-expression and the Mitotic Activity Index (MAI) in the series of breast cancer samples (Fig 5B), implying an anti-proliferative effect of KLF9. In vitro, upregulation of KLF9 expression was shown in MDA-MB-231 cells in a confluency-dependent manner with limited expression in subconfluent cultures (60% - 80%) and a 3-fold rise of KLF9 mRNA in confluent cultures, corroborating the findings in clinical samples (Fig 5C).