. 2013 Jun 5;105(14):1043–1049. doi: 10.1093/jnci/djt124

Table 4.

Breast cancer risk associated with benign breast disease cross-classified with breast density

Benign breast disease	BI-RADS breast density, HR (95% CI)*
Benign breast disease	Almost entirely fat	Scattered fibroglandular densities	Heterogeneously dense	Extremely dense
Nonproliferative	0.85 (0.56 to 1.28),	1.0 (reference)	1.51 (1.28 to 1.78),	2.15 (1.73 to 2.68),
Nonproliferative	P = .44		P < .001	P < .001
Proliferative without atypia	0.67 (0.30 to 1.52),	1.37 (1.11 to 1.69),	2.02 (1.68 to 2.44),	2.05 (1.54 to 2.72),
Proliferative without atypia	P = .34	P = .003	P < .001	P < .001
Atypical hyperplasia	0.68 (0.09 to 4.90),	2.57 (1.85 to 3.58),	3.37 (2.58 to 4.40),	5.34 (3.52 to 8.09),
Atypical hyperplasia	P = .70	P < .001	P < .001	P < .001

* Using the Breast Imaging Reporting and Data System (BI-RADS) density categories: 1 = almost entirely fat (low density); 2 = scattered fibroglandular densities (average density); 3 = heterogeneously dense (high density); 4 = extremely dense (very high density). The hazard ratios are relative to women with nonproliferative breast pathology and scattered fibroglandular densities and are adjusted for age, race/ethnicity, and registry. The P value for interaction between benign breast disease and breast density = 0.28, based on a two-sided Wald test.