Table 3.
Adjusted hazard ratios for invasive breast cancer by breast density (BI-RADS/longitudinal): subgroup with ≥ 3 mammograms
| Model | Density measure | Adjusted hazard ratio (95% CI) (time-varying breast density covariate) |
Adjusted hazard ratio (95% CI) (breast density at/to third mammogram) |
|
|---|---|---|---|---|
| 1 | BI-RADS density | |||
| Fatty | 0.52 (0.42–0.65) | 0.52 (0.40–0.67) | ||
| Scattered | 1 [Reference] | 1 [Reference] | ||
| Heterogeneous | 1.58 (1.43–1.74) | 1.57 (1.42–1.74) | ||
| Extremely dense | 1.82 (1.55–2.14) | 2.06 (1.77–2.40) | ||
| ΔLR-χ2 (df = 3) = 186.7 | ΔLR-χ2 (df = 3) = 175.9 | |||
| 2 | Continuous longitudinal density | |||
| Linear (per unit*) | 5.62 (3.25–9.72) | 4.99 (2.81–8.84) | ||
| Quadratic (per unit2*) | 0.82 (0.74–0.90) | 0.84 (0.76–0.94) | ||
| ΔLR-χ2 (df = 2) = 251.2 | ΔLR-χ2 (df = 2) = 252.0 | |||
| 3 | Categorical longitudinal density | |||
| Category 1: | ‘Fatty’ I (< 1.5) | 0.47 (0.35–0.63) | 0.45 (0.32–0.62) | |
| Category 2: | ‘Fatty’ II (1.5 to < 2.0) | 0.73 (0.60–0.89) | 0.79 (0.63–0.98) | |
| Category 3: | ‘Scattered’ I (2.0 to < 2.2) | 1 [Reference] | 1 [Reference] | |
| Category 4: | ‘Scattered’ II (2.2 to < 2.6) | 1.24 (1.06–1.45) | 1.34 (1.15–1.56) | |
| Category 5: | ‘Heterogeneous’ I (2.6 to < 2.9) | 1.58 (1.36–1.84) | 1.73 (1.49–2.01) | |
| Category 6: | ‘Heterogeneous’ II (2.9 to < 3.2) | 1.98 (1.70–2.32) | 2.09 (1.79–2.44) | |
| Category 7: | ‘Extremely dense’ I (3.2 to < 3.6) | 2.25 (1.84–2.75) | 2.31 (1.89–2.82) | |
| Category 8: | ‘Extremely dense’ II (≥ 3.6) | 2.27 (1.81–2.86) | 2.92 (2.36–3.62) | |
| ΔLR-χ2 (df = 7) = 246.3 | ΔLR-χ2 (df = 7) = 242.2 | |||
n = 76,313 (subgroup of women with at least 3 mammograms); follow-up from the third mammogram
Adjusted hazard ratios from proportional-hazards Cox models for BI-RADS density (time-varying or at third mammogram) or the new longitudinal breast density measure (time-varying or to third mammogram) as a continuous or eight-category value
Hazard ratios adjusted for age at baseline (in this instance, where follow-up started at the third mammogram, age at third mammogram was used) (continuous) and BMI (continuous; time-varying or at third mammogram)
‘Time-varying’ means that a woman’s values for breast density and BMI are updated through time, i.e. at each screening examination
Cut points for the eight-category new breast density are the same as those used in Table 2
95% CIs from Wald tests
ΔLR-χ2 represents the additional information in the likelihood-ratio statistic when including breast density
BI-RADS Breast Imaging Reporting and Data System, BMI body mass index, df degrees of freedom, 95% CI 95% confidence interval
*Units of longitudinal density are non-standard—interpretation may be facilitated by Fig. 1