Table 1.

Study participant characteristics among 452 breast cancer cases and 902 controls, Sister Study, 2003–2009

Breast cancer casesControls
Age at enrollment, mean (y; SD)46.8(4.4)46.8(4.4)
Age at menarche, y
 <128619.017819.7
 1213329.423926.5
 1313129.024326.9
 ≥149420.824026.6
Currently using oral contraceptives, N (%)
 No40489.483993.0
 Yes4810.6637.0
Smoking status, N (%)
 Never28863.755461.4
 Former13830.527230.2
 Current265.8768.4
Parity and breastfeeding, N (%)
 Nulliparous11325.019621.7
 Parous, never breastfed7015.513214.6
 Parous, breastfed26959.557363.5
BMI (kg/m2), N (%)
 <18.540.9141.6
 18.5–24.920545.439744.0
 25–29.913730.324827.5
 ≥3010623.524226.8
Total testosterone (ng/dL), N (%)
 ≤209019.920422.6
 20.1–2711826.123626.2
 27.1–3511926.323125.6
 ≥35.111625.721924.3
 Undetectable/insufficient sample92.0121.3
Hysterectomy, N (%)a
 No39487.277786.1
 Yes5812.812513.9
Unilateral oophorectomy, N (%)a
 No43195.484894.0
 Yes214.6546.0
Polycystic ovary syndrome (PCOS), N (%)
 No43496.087296.7
 Yes184.0273.0
  • aAll women were required to have ≥1 intact ovary for selection into the nested case–control study.