Focussing on breast cancer, levels of specific miRNAs differ between malignant and normal breast tissue and are able to classify tumours according to clinicopathological variables, such as proliferation index, steroid hormone receptor and Her2/neu status, nodal status and tumour stage (Iorio et al, 2005; Mattie et al, 2006; Lowery et al, 2008). This evidence concerns the gene ERBB2 and breast carcinoma.