Table 3 Adjusted hazard ratios for invasive breast cancer by breast density (BI-RADS/longitudinal): subgroup with ≥ 3 mammograms

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