Table 1.

Characteristics of participants in the study

OverallMCCSABCFR
Number of women (number of mammograms)1,064 (4,714)846 (3,951)218 (763)
Number of mammograms per woman, median (range)4 (1–14)5 (1–10)3 (1–14)
Number of women with one mammogram, n (%)141 (13)80 (9)61 (28)
Mean (SD)
Time interval between mammograms, y2.2 (1.0)2.2 (0.8)2.2 (1.7)
Age at first mammogram, y55.8 (9.8)58.9 (7.6)44.0 (8.3)
Age at last mammogram, y63.4 (10.7)67.0 (7.8)49.4 (8.7)
BMI at study entry, kg/m226.8 (5.1)27.5 (5.1)24.1 (4.3)
BMI at first mammogram, kg/m227.0 (5.6)27.5 (5.1)24.8 (6.9)
BMI at last mammogram, kg/m226.8 (5.1)27.5 (5.1)24.1 (4.3)
Median (25th–75th percentile)
Time between first and last mammograms, y8.0 (5.0)8.4 (4.9)4.5 (4.8)
At first mammogram:
 DA, cm214.7 (4.5–30.3)12.0 (3.3–26.7)25.0 (14.4–38.0)
 NDA, cm2116.0 (77.6–161.1)122.6 (85.6–170.7)83.2 (57.6–132.7)
 Total area, cm2135.3 (100.6–179.7)139.3 (107.8–187.7)118.0 (82.1–162.5)
 Percent density, %11.7 (3.0–26.1)8.7 (2.3–21.8)24.1 (12.3–34.7)
At last mammogram:
 DA, cm212.1 (3.5–25.7)9.7 (2.8–21.7)23.6 (11.4–36.6)
 NDA, cm2131.0 (91.0–178.2)138.7 (99.6–186.7)93.7 (60.0–139.0)
 Total area, cm2148.3 (110.4–195.6)154.3 (118.1–200.9)123.6 (83.8–165.9)
 Percent density, %8.5 (2.4–20.4)6.7 (1.6–16.7)21.2 (8.7–31.4)
Difference between first and last mammogram
 DA, cm2−0.7 (−6.0 to 0.6)−0.9 (−5.5 to 0.4)−0.4 (−8.1 to 2.9)
 NDA, cm211.2 (0–27.9)13.1 (0–30.4)0.7 (−4.4 to 18.7)
 Total area, cm28.5 (−1.2 to 24.4)10.3 (−0.4 to 26.8)0.0 (−4.5 to 13.4)
 Percent density, %−0.9 (−6.1 to 0.1)−1.0 (−5.3 to 0.1)−0.5 (−9.6 to 2.3)
N (%)
Case–control statusa
 Cases155 (15)149 (18)6 (3)
 Controls909 (85)697 (82)212 (97)
Menarche
 ≤12382 (36)311 (37)71 (33)
 13+680 (64)533 (63)147 (67)
Parity
 Nulliparous120 (11)107 (13)13 (6)
 Multiparous908 (85)739 (87)169 (78)
Family history (number of women)
 Yes318 (37)149 (22)169 (100)
 No541 (63)541 (78)0 (0)
  • aCase–control status of participants refers to the status at selection of the nested case–control mammographic density study.