Table 2.

Updated meta-analysis of the association between breast density and the incidence of invasive breast cancer in general populations^*

Method of breast density measurement	Category	RR (95% CI)
Wolfe grade†	N1 (fatty)	1 (reference)
	P1	1.76 (1.41 to 2.19)
	P2	3.05 (2.54 to 3.66)
	Dy (most dense)	3.98 (2.53 to 6.27)
BI-RADS	1 (fatty)	1 (reference)
	2 (scattered densities)	2.03 (1.61 to 2.56)
	3 (heterogeneously  dense)	2.95 (2.32 to 3.73)
	4 (extremely dense)	4.03 (3.10 to 5.26)
% Of breast area  that is dense	<5	1 (reference)
	5–24	1.74 (1.50 to 2.03)
	25–49	2.15 (1.87 to 2.48)
	50–74	2.92 (2.55 to 3.34)
	≥75	4.20 (3.61 to 4.89)

^*The meta-analysis by McCormack et al. (29) was included in this meta-analysis. All studies were adjusted for age; studies that further adjust for body mass index or weight observed somewhat stronger associations. CI = confidence interval; BI-RADS = Breast Imaging Reporting and Data System; RR = relative risk.

^†Wolfe grades: N1 = normal fatty breast, P1 = prominent ducts occupy less than 25% of the breast image; P2 = prominent ducts occupy 25%–75%; Dy = dysplastic breast with sheets of dense parenchyma.