Background: Human papillomavirus and hormonal contraceptives may be risk factors for cervical precancer and malignant breast tumours.
Methods: Standardised incidence ratios (SIRs) of malignant breast tumours during 1970-2008 were estimated separately for women with prior squamous and glandular cervical precancer.
Results: Women with squamous precancer and women with glandular precancer in the cervix had a significantly higher risk of malignant breast tumours than the general female population (SIR, 95% confidence interval: 1.10, 1.05-1.14 and 1.52, 1.11-2.08, respectively).
Interpretation: Shared risk factors or screening attendance may explain the excess risk of malignant breast tumours among women with a history of cervical precancer.