In breast cancer, the expression of known prognostic and predictive factors such ER (oestrogen receptor), PR (progesterone receptor) and HER2 (human epidermal growth factor receptor 2) were reliably analysed on TMA (Kononen et al, 1998; Camp et al, 2000; Gillett et al, 2000; Torhorst et al, 2001), but it is still unclear as to how representative TMA is when molecules that show focal localisation within the tumour are studied (Gillett et al, 2000). This evidence concerns the gene ERBB2 and breast carcinoma.