Table 2 Adjusted hazard ratios for invasive breast cancer by BI-RADS density or longitudinal breast density (continuous/categorical)

1

BI-RADS density

 Fatty

0.49 (0.40–0.60)

 Scattered

1 [Reference]

 Heterogeneous

1.71 (1.56–1.86)

 Extremely dense

2.11 (1.84–2.42)

ΔLR-χ² (df = 3) = 307.7

2

Continuous longitudinal density

 Linear (per unit*)

5.53 (3.34–9.14)

 Quadratic (per unit²*)

0.83 (0.76–0.92)

ΔLR-χ² (df = 2) = 379.6

3

Categorical longitudinal density

 Category 1:

‘Fatty’ I (< 1.5)

0.48 (0.36–0.63)

 Category 2:

‘Fatty’ II (1.5 to < 2.0)

0.83 (0.69–1.00)

 Category 3:

‘Scattered’ I (2.0 to < 2.2)

1 [Reference]

 Category 4:

‘Scattered’ II (2.2 to < 2.6)

1.43 (1.24–1.64)

 Category 5:

‘Heterogeneous’ I (2.6 to < 2.9)

1.82 (1.59–2.07)

 Category 6:

‘Heterogeneous’ II (2.9 to < 3.2)

2.44 (2.11–2.81)

 Category 7:

‘Extremely dense’ I (3.2 to < 3.6)

2.66 (2.23–3.17)

 Category 8:

‘Extremely dense’ II (≥ 3.6)

3.03 (2.48–3.70)

ΔLR-χ² (df = 7) = 375.1