Nevertheless recent data show that some invasive breast cancers expressing the basal cytokeratin CK5/6, may represent one ERα-negative subset, known as the basal epithelial phenotype and show a relatively poor prognosis (Perou et al, 2000; Sorlie et al, 2001, 2003; Nielsen et al, 2004). The gene discussed is KRT5; the disease is breast cancer.