Different kinase-defective isoforms of BTK have been reported in B-cell precursor leukaemia cells,4 and an 80-kDa isoform, bearing an extended N-term domain, has been demonstrated in breast carcinoma cells24 and at least three other protein-coding splice variants can be predicted by the Ensembl automatic gene annotation system (http://www.ensembl.org/Homo_sapiens/Transcript/Summary?db=core;g=ENSG00000010671;r=X:101349447-101386224;t=ENST00000621635). Here, BTK is linked to breast carcinoma.