However, because of the overwhelmingly high rate of the ductal histological type among breast cancers, there is need to improve the definition of true recurrences by using new biological tools of clonal relation such as pan-genomic profiles (Waldman et al, 2000), loss of heterozygosity (Schlechter et al, 2004; Vicini et al, 2007), p53 mutation analysis (van der Sijp et al, 2002) or the inactivation of the X chromosome (Shibata et al, 1996). The gene discussed is TP53; the disease is breast cancer.