miR-155 expression in hMLH1-negative tumors. miR-155 expression was assessed by in situ hybridization on paraffin-embedded tissues. (A) CR-78 cancer tissue (with unknown causes of MLH1 loss) showing strong miR-155 expression (large arrow), with stroma (small arrow) negative for miR-155 expression. (B) CR-79 tissue (MLH1 loss due to promoter methylation) showing faint expression of miR-155 only in inflammatory cells (large arrow), with no signal detected in cancer tissue (small arrow).