Loss of the wild-type BRCA1 or BRCA2 allele has been shown in breast tumours arising in patients carrying a germline mutation in one of these genes (Collins et al, 1995; Cornelis et al, 1995; Merajver et al, 1995; Osorio et al, 2002) and in some sporadic breast tumours (Hanby et al, 2000; Katsama et al, 2000; Johnson et al, 2002). Here, BRCA1 is linked to breast neoplasm.