Table 2.

HRs of second breast cancers by four measures of mammographic density

Density measureFull cohortAny second breast cancerSecond breast cancer (invasive only)
UnadjustedAdjusted*UnadjustedAdjusted*
NNHR (95% CI)HR* (95% CI)PNHR (95% CI)HR* (95% CI)P
Parenchymal pattern
    N197151.01.00.06101.01.00.44
    P1209511.7 (0.9-3.0)1.7 (0.9-3.0)301.5 (0.7-3.0)1.5 (0.7-3.1)
    P26081571.8 (1.1-3.1)1.8 (1.0-3.2)801.4 (0.7-2.7)1.5 (0.8-3.1)
    DY2152.2 (0.8-6.1)2.0 (0.7-5.8)10.7 (0.1-5.3)0.7 (0.1-5.5)
Area of density
    Quintile 1185341.01.00.02201.01.00.02
    Quintile 2193491.5 (1.0-2.3)1.5 (1.0-2.4)261.4 (0.8-2.4)1.4 (0.8-2.6)
    Quintile 3190451.4 (0.9-2.2)1.4 (0.9-2.2)221.2 (0.6-2.2)1.3 (0.7-2.5)
    Quintile 4184441.4 (0.9-2.2)1.3 (0.8-2.1)221.2 (0.6-2.2)1.2 (0.6-2.3)
    Quintile 5183561.9 (1.3-3.0)1.8 (1.2-2.9)311.8 (1.0-3.2)2.1 (1.2-3.8)
Percent density
    066111.01.00.1981.01.00.48
    1-24298681.4 (0.8-2.7)1.5 (0.8-2.8)381.1 (0.5-2.4)1.2 (0.5-2.5)
    25-49314781.6 (0.9-3.1)1.7 (0.9-3.3)411.2 (0.6-2.6)1.4 (0.6-3.1)
    50-74225641.9 (1.0-3.6)1.9 (0.9-3.7)301.2 (0.6-2.7)1.4 (0.6-3.3)
    ≥753271.4 (0.5-3.5)1.3 (0.5-3.6)41.0 (0.3-3.5)1.2 (0.3-4.4)
BI-RADS density
    Almost all fat165281.01.00.03161.01.00.16
    Scattered fibroglandular292711.5 (1.0-2.4)1.6 (1.0-2.5)391.5 (0.8-2.6)1.6 (0.9-3.0)
    Heterogeneously dense328911.7 (1.1-2.6)1.8 (1.1-2.8)501.6 (0.9-2.9)1.9 (1.0-3.6)
    Extremely dense125361.8 (1.1-3.0)1.9 (1.0-3.3)151.3 (0.7-2.7)1.6 (0.7-3.6)
  • *Adjusted for age (continuous), BMI (<20, 20 to <25, 25 to <30, 30 to <35, ≥35), radiotherapy (yes, no), tamoxifen (yes, no), and diagnosis year (1990-1991, 1992-1993, 1994-1995, 1996-1997).

  • P-value for linear trend.