Tumours with the highest cyclin B1 expression (>10%) were more frequent among BRCA1 than sporadic (OR 2.8, 95% CI 1.4–5.6, P=0.003) or familial BRCA1/2 mutation negative (OR 4.8, 95% CI 2.3–9.9, P<0.0005) patients. The gene discussed is BRCA1; the disease is neoplasm.