Table 2.

Relative Risk of Invasive Breast Cancer by Breast Density and Age and Prevalence of Density by Age Group

Age Group	BI-RADS Density	Breast Density–Related Risk*	Prevalence of Density Level within Age Group
40–49	A	0.37	0.05
	B	0.72	0.35
	C	1.16	0.46
	D	1.46	0.13
50–64	A	0.50	0.09
	B	0.84	0.46
	C	1.25	0.38
	D	1.53	0.07
65–74	A	0.61	0.13
	B	0.94	0.53
	C	1.28	0.31
	D	1.45	0.03

Note: the base models include average population density. When density is explicitly included for specific analyses, these data are used to modify incidence. In density-specific analyses, density also modifies mammography performance.

^*Referent group is average population density

Density a refers to entirely fatty; b to scattered density; c to heterogeneously dense, and d to extremely dense

Source: Breast Cancer Surveillance Consortium. (24)