Table 3. Rates of Early and Advanced Cancer by Breast Density and Age.

Breast Density by Decade of Age	Prevalence in Population, %	Early Cancer (n = 3665)		Advanced Cancer (n = 741)
		Rate of Stage I or IIA Screen-Detected Invasive Cancer per 1000 Examinations (95% CI)	Expected Stage I or IIA Screen-Detected Invasive Cancers in 100 000 Screened Women, No. (%)	Rate of Stage IIB or Higher Invasive Cancer per 1000 Examinations (95% CI)	Expected Stage IIB or Higher Invasive Cancer in 100 000 Screened Women, No. (%)
40-49 Years of Age
Almost entirely fatty	1.5	0.5 (0.3-0.9)	0.74 (0.35)	0.09 (0.02-0.45)	0.14 (0.33)
Scattered areas of fibroglandular densities	8.1	1.1 (0.9-1.4)	9.0 (4.3)	0.21 (0.14-0.31)	1.70 (4.0)
Heterogeneously dense	12.5	1.2 (1.0-1.4)	15.0 (7.1)	0.42 (0.30-0.57)	5.3 (12.6)
Extremely dense	3.8	1.0 (0.8-1.3)	3.8 (1.8)	0.56 (0.42-0.74)	2.1 (5.0)
50-59 Years of Age
Almost entirely fatty	3.7	0.9 (0.7-1.1)	3.3 (1.6)	0.11 (0.06-0.21)	0.41 (1.0)
Scattered areas of fibroglandular densities	14.8	1.7 (1.5-2.0)	25.2 (11.9)	0.36 (0.28-0.47)	5.3 (12.6)
Heterogeneously dense	14.1	2.0 (1.8-2.2)	28.3 (13.4)	0.44 (0.35-0.55)	6.2 (14.8)
Extremely dense	2.8	1.8 (1.4-2.2)	5.1 (2.4)	0.77 (0.58-1.02)	2.2 (5.2)
60-69 Years of Age
Almost entirely fatty	4.3	2.2 (1.8-2.7)	9.4 (4.4)	0.20 (0.13-0.32)	0.86 (2.0)
Scattered areas of fibroglandular densities	14.3	3.2 (2.9-3.6)	45.9 (21.7)	0.39 (0.32-0.49)	5.6 (13.3)
Heterogeneously dense	9.6	3.2 (2.8-3.6)	30.9 (14.6)	0.67 (0.53-0.85)	6.4 (15.2)
Extremely dense	1.2	1.9 (1.2-3.0)	2.4 (1.1)	0.70 (0.46-1.08)	0.84 (2.0)
70-74 Years of Age
Almost entirely fatty	1.4	2.9 (2.4-3.4)	4.2 (2.0)	0.23 (0.12-0.46)	0.32 (0.76)
Scattered areas of fibroglandular densities	4.8	3.3 (2.8-3.9)	15.8 (7.5)	0.48 (0.32-0.71)	2.3 (5.5)
Heterogeneously dense	2.7	4.2 (3.5-4.9)	11.4 (5.4)	0.82 (0.60-1.12)	2.2 (5.2)
Extremely dense	0.3	3.5 (2.2-5.6)	0.93 (0.44)	0.51 (0.15-1.67)	0.15 (0.36)