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Table 1 Baseline characteristics of the study group (72 breast cancer cases and 486 controls from the placebo arm of IBIS-I)

From: Mammographic breast density refines Tyrer-Cuzick estimates of breast cancer risk in high-risk women: findings from the placebo arm of the International Breast Cancer Intervention Study I

Variable Controls Cases
(n =486) (n =72)
Follow-up (years) 11.6 (10.7-12.3) 5.1 (3.1-7.9)
Age (years) 49.5 (46.4-54.4) 49.9 (46.3-56.0)
BMI (kg/m 2 ) 25.8 (23.4-29.1) 26.2 (23.7-28.4)
Menopausal status   
Pre/peri 261 (54%) 38 (53%)
Post 225 (46%) 34 (47%)
HRT use   
Never 316 (65%) 46 (64%)
Current 108 (22%) 14 (19%)
Previous 62 (13%) 12 (17%)
Age at menarche (years) 13 (12-14) 13 (12-14)
Age at first birth   
Nulliparous 69 (14%) 12 (17%)
>29 years 55 (11%) 6 (8%)
26-29 years 98 (20%) 14 (19%)
21-25 years 178 (37%) 27 (38%)
<21 years 86 (18%) 13 (18%)
Tyrer-Cuzick risk score   
10-year absolute risk (%) 5.5 (4.5-6.7) 5.4 (4.1-6.9)
10 -year relative risk 2.2 (1.8-2.7) 2.1 (1.7-2.9)
Mammographic density   
Percent dense area (%) 42.5 (15.0-70.0) 62.5 (25.0-80.0)
  1. Median (interquartile range). BMI, body mass index; HRT, hormone replacement therapy.