High BRE and high EVI1 expression are mutually exclusive in MLL-AF9 leukemia. (A) BRE expression was plotted against EVI1 expression for MLL-AF9 positive cases in 2 separate MLL-AF9 cohorts.^7,8  In the first cohort (left plot), 33% (6/18) of the samples showed high EVI1 expression, and 55.6% (10/18) showed high BRE expression. In the second cohort (right plot), 27.3% of the samples showed high EVI1 expression (3/11), and 54.5% showed high BRE expression (6/11). Both cohorts contained 2 patients with neither high BRE nor high EVI1 expression. High BRE expression was defined as described before.³  High EVI1 expression was defined as the expression of the upper 10% of the total cohort. P values for negative correlations were calculated using Spearman correlation tests. (B) EVI1-positive patients cluster apart from high BRE expressing patients among MLL-AF9 positive patients in unsupervised clustering analysis. However, EVI1-positive patients show less similar expression profiles among each other compared with high BRE expressing patients (indicated by faint red color compared with bright red color, respectively). Unsupervised clustering was performed on the first cohort as described elsewhere⁹  and clustering is represented as pairwise correlations between samples with a gradient from red to blue indicating degree of correlation (bright red: high correlation, blue: poor correlation). Black bars represent relative BRE (212645_x_at) and EVI1 (221884_at) expression, as indicated.