HOXA9 and leukemia: Analysis of the selected Hox A cluster and Hox cofactor genes revealed a high degree of co-expression between these in leukemia samples, where correlation coefficient between HOXA5, HOXA7, HOXA9 and MEIS1 ranged between 0.83 and 0.92 (Spearman rank correlation, p<0.0001 in all cases, e.g. in Figure 3A).