Table 1.

Selected characteristics of all subjects (n = 1,020) by case-control status

Cases (n = 364)Controls
Matched by machine (n = 359)P*Not matched by machine (n = 297)P*
Risk factors
    Height (cm)162.6 (6.9)163.1 (6.6)0.32163.4 (6.2)0.12
    Weight (kg)68.3 (14.4) n = 36268.0 (14.6) n = 3580.7568.3 (14.7)0.96
    BMI (kg/m2)25.8 (5.2) n = 36225.6 (5.5) n = 3580.5025.6 (5.2)0.47
    Age at mammogram (y)59.6 (11.0)59.5 (11.0)0.9058.4 (11.1)0.17
    Age at menarche (y)12.7 (1.4) n = 36112.8 (1.5)0.5112.7 (1.4) n = 2950.93
    Parity (% parous)70.976.00.1269.70.74
    Age at birth of 1st child (y)26.3 (5.0) n = 25826.6 (5.4) n = 2740.5326.6 (5.6) n = 2060.54
    No. of live births1.7 (1.4)1.8 (1.4)0.201.6 (1.4)0.76
    Menopausal status (% postmenopausal)68.0 (n = 363)69.90.5969.6 (n = 296)0.67
    Age at menopause (y)49.4 (6.2) n = 21147.7 (6.4) n = 2200.0148.1 (6.5) n = 1780.05
    HRT ever used (% yes)45.145.5 (n = 358)0.9044.40.88
    Years HRT used (y)4.0 (6.9)4.2 (7.5) n = 3580.693.8 (7.0)0.73
    Breast cancer in 1st degree relatives (% yes)21.6 (n = 361)26.3 (n = 357)0.1423.0 (n = 296)0.68
Imaging parameters
    Breast thickness (cm)5.4 (1.2)5.4 (1.4)0.925.4 (1.4)0.57
    KVP26.8 (2.0)26.7 (2.0)0.6226.8 (2.1)0.81
    MAS155.3 (48.7)156.0 (57.9)0.85144.9 (52.4)0.01
    Compression force (N)104.7 (32.6)103.9 (31.8)0.74101.3 (33.0)0.20
Volume breast measurements
    Percent dense volume (%)11.3 (16.1)9.9 (14.6)0.237.7 (12.9)0.001
    Dense volume (cm3)57.9 (76.6)53.6 (86.5)0.2538.9 (60.4)0.0001
    Total volume (cm3)725.2 (360.8)761.6 (417.2)0.44752.7 (406.8)0.58
Area breast measurements
    Percent dense area (%)33.3 (20.5)30.3 (19.7)0.0730.1 (19.9)0.05
    Dense area (cm2)40.8 (26.9)38.4 (27.3)0.2136.3 (23.4)0.04
    Total area (cm2)141.5 (61.0)146.4 (64.2)0.31144.6 (63.4)0.55
  • NOTE: Shown are mean (SD) and percentage for, respectively, continuous and categorical variables.

  • HRT, hormone replacement therapy; KVP, kilovoltage peak; MAS, milliampere seconds.

  • * Two-sided two-sample t test for continuous variables, and χ2 test for categorical variables. Cubic root and square root transformations were applied to, respectively, volume and area breast measurements.