Table 1.

Established hormone-related risk factors for premenopausal breast cancer

Risk factor	Higher risk group
Age at menarche	Early age at menarche
Age at first birth	Later age at first birth
Parity	Nulliparous or fewer childrena
Premenopausal body mass index (kg/m2)	Low body mass index
Childhood body size	Small body size/lean
Breast feeding	No breast feeding (or shorter durations)
Mammographic density	Higher density

^aParity infers a short term (<1 decade) increase in risk, followed by a long-term decrease in risk

References: Hankinson SE et al. 2004 4. Breast Cancer Res: 6(5): 213–218; de Waard F, Thijssen JH. 2005 8. J Steroid Biochem Mol Biol: 97(5): 451–458