Table 2.

Mammographic density measurements by known breast cancer risk factors, mammographic view, and case status at time of mammography

Risk factorN (%)PD (%)Dense area, cm2Nondense area, cm2
CategoriesMean (95% CI)Mean (95% CI)Mean (95% CI)
Age,a y
 <40366 (2.2)34.2 (30.3–38.3)36.8 (31.9–42.1)75.1 (66.8–83.8)
 40–492,794 (16.5)28.2 (25.3–31.4)33.0 (29.1–37.1)89.7 (82.9–96.8)
 50–596,486 (38.4)20.3 (17.9–22.9)26.4 (23.0–30.0)112.2 (104.8–119.8)
 60–695,670 (33.6)14.9 (12.8–17.2)21.3 (18.2–24.6)130.2 (122.2–138.4)
 ≥701,579 (9.3)13.0 (11.0–15.2)17.3 (14.5–20.4)143.0 (134.1–152.3)
P<0.001<0.001<0.001
BMI,b kg/m2
 <257,355 (44.1)25.8 (23.2–28.6)27.0 (23.6–30.7)82.9 (77.1–89.0)
 ≥259,334 (55.9)14.8 (12.8–16.9)23.3 (20.1–26.7)144.3 (136.6–152.3)
P<0.001<0.001<0.001
Menopausal statusc
 Pre- or perimenopausal3,690 (22.2)21.5 (19.1–24.1)27.1 (23.6–30.8)113.5 (106.4–120.9)
 Postmenopausal12,964 (77.8)18.4 (16.2–20.7)24.1 (20.9–27.5)116.3 (109.3–123.5)
P<0.001<0.0010.05
PMH use (at ages ≥ 55)c
 Never4,800 (48.6)14.6 (12.5–16.9)20.2 (16.7–23.9)129.1 (120.4–138.2)
 Ever5,067 (51.4)17.8 (15.5–20.4)23.6 (19.9–27.7)122.7 (114.2–131.6)
P<0.001<0.001<0.001
Parityc
 Nulliparous1,781 (10.7)22.6 (20.1–25.2)29.0 (25.4–32.9)109.2 (102.2–116.4)
 Parous14,808 (89.3)18.7 (16.5–21.0)24.3 (21.1–27.7)116.7 (109.8–123.8)
P<0.001<0.001<0.001
Mammographic viewc
 CC6,051 (35.8)17.7 (14.2–21.5)25.1 (19.7–31.1)122.4 (111.1–134.2)
 MLO10,844 (64.2)20.1 (17.3–23.2)24.8 (20.6–29.4)111.5 (103.2–120.2)
P0.30.90.1
Case statusd
 BC case4,530 (37.8)24.5 (20.8–28.4)30.0 (24.1–36.4)108.2 (95.6–121.5)
 Noncase7,439 (62.2)19.3 (16.0–22.8)24.2 (19.0–30.1)117.9 (104.9–131.7)
P<0.001<0.001<0.001

Abbreviations: BC, breast cancer; CC, craniocaudal; MLO, mediolateral oblique.

  • aAdjusted for study.

  • bAdjusted for study and age.

  • cAdjusted for study, age, and BMI.

  • dRestricted to 9 studies that recruited both cases and noncases and adjusted for study, age, and BMI.