In terms of isoform expression pattern, all our data corroborate the hypothesis that the truncated transcript starting from intron5 is a tumour-specific isoform: this short WT1 variant was first detected in the blood of patients affected by acute leukaemia, then in breast and pancreatic cancer cell lines43, 56 and we have now shown that it is expressed in human breast cancer biopsies, but is absent in the healthy mammary gland. Here, WT1 is linked to breast carcinoma.