Table 1 Characteristic of the study population (n = 279,967), by breast density category (number [percentage])
Characteristics | Almost entirely fat (BI-RADS I) n = 30,249 | Scattered fibroglandular densities (BI-RADS II) n = 116,666 | Heterogeneously dense (BI-RADS III) n = 110,181 | Extremely dense (BI-RADS IV) n = 22,871 |
|---|---|---|---|---|
Age at mammogram, years | ||||
40–49 | 4526 (15.0) | 27,195 (23.3) | 38,172 (34.6) | 11,261 (49.2) |
50–59 | 9548 (31.6) | 37,768 (32.4) | 37,004 (33.6) | 7432 (32.5) |
60–69 | 8749 (28.9) | 28,004 (24.0) | 19,960 (18.1) | 2536 (11.1) |
70–79 | 5388 (17.8) | 16,712 (14.3) | 10,331 (9.4) | 1069 (4.7) |
80–89 | 2038 (6.7) | 6987 (6.0) | 4714 (4.3) | 573 (2.5) |
Race/ethnicity | ||||
White | 25,879 (85.6) | 101,078 (86.6) | 92,698 (84.1) | 18,170 (79.4) |
Black | 703 (2.3) | 2031 (1.7) | 1873 (1.7) | 352 (1.5) |
Asian/Pacific Islander | 842 (2.8) | 4085 (3.5) | 7416 (6.7) | 2662 (11.6) |
American Indian | 117 (0.4) | 442 (0.4) | 373 (0.3) | 45 (0.2) |
Hispanic | 2056 (6.8) | 6248 (5.4) | 5122 (4.6) | 1115 (4.9) |
Mixed/other | 652 (2.2) | 2782 (2.4) | 2699 (2.4) | 527 (2.3) |
Body mass index, kg/m2 | ||||
≤18.4 | 142 (0.5) | 956 (0.8) | 1808 (1.6) | 1198 (5.2) |
18.5–24.9 | 5383 (17.8) | 36,175 (31.0) | 53,604 (48.7) | 15,974 (69.8) |
25.0–29.9 | 8846 (29.2) | 38,576 (33.1) | 33,316 (30.2) | 4283 (18.7) |
30.0–34.9 | 7548 (25.0) | 23,267 (19.9) | 13,803 (12.5) | 1038 (4.5) |
35.0–39.9 | 4361 (14.4) | 10,501 (9.0) | 5028 (4.6) | 273 (1.2) |
≥40 | 3969 (13.1) | 7191 (6.2) | 2622 (2.4) | 105 (0.5) |
Age at menarche, years | ||||
≤12 | 14,400 (47.6) | 51,281 (44.0) | 44,093 (40.0) | 7989 (34.9) |
13 | 9211 (30.5) | 37,191 (31.9) | 35,622 (32.3) | 7516 (32.9) |
14 | 3626 (12.0) | 15,203 (13.0) | 15,816 (14.4) | 3682 (16.1) |
≥15 | 3012 (10.0) | 12,991 (11.1) | 14,650 (13.3) | 3684 (16.1) |
Parity/age at first child | ||||
Nulliparous | 4019 (13.3) | 14,264 (12.2) | 18,085 (16.4) | 5727 (25.0) |
Parous/≤29 years | 23,317 (77.1) | 88,215 (75.6) | 74,309 (67.4) | 11,896 (52.0) |
Parous/≥30 years | 2913 (9.6) | 14,187 (12.2) | 17,787 (16.1) | 5248 (22.9) |
Menopausal status/HRT | ||||
Premenopausal | 3776 (12.5) | 24,161 (20.7) | 35,502 (32.2) | 10,855 (47.5) |
Postmenopausal/current HRT use | 3064 (10.1) | 14,627 (12.5) | 15,995 (14.5) | 2840 (12.4) |
Postmenopausal/no current HRT use | 22,908 (75.7) | 75,358 (64.6) | 55,548 (50.4) | 8378 (36.6) |
Perimenopausal | 501 (1.7) | 2520 (2.2) | 3136 (2.8) | 798 (3.5) |
Family history of breast cancer | ||||
Yes | 5099 (16.9) | 19,787 (17.0) | 18,946 (17.2) | 3860 (16.9) |
No | 25,150 (83.1) | 96,879 (83.0) | 91,235 (82.8) | 19,011 (83.1) |
History of breast biopsy | ||||
Yes | 5250 (17.4) | 23,387 (20.0) | 26,687 (24.2) | 6255 (27.3) |
No | 24,999 (82.6) | 93,279 (80.0) | 83,494 (75.8) | 16,616 (72.7) |
Residential area | ||||
Urban | 17,673 (59.1) | 63,393 (54.6) | 72,210 (65.6) | 14,933 (65.4) |
Rural | 12,244 (40.9) | 52,816 (45.4) | 37,794 (34.4) | 7916 (34.6) |
Median household income | ||||
≤US$46,075 | 8811 (29.1) | 33,011 (28.3) | 24,474 (22.2) | 4591 (20.1) |
US$46,076–54,093 | 7871 (26.0) | 31,185 (26.7) | 25,607 (23.2) | 5324 (23.3) |
US$54,094–66,322 | 7051 (23.3) | 28,168 (24.1) | 30,237 (27.4) | 5897 (25.8) |
≥US$66,323 | 6516 (21.5) | 24,302 (20.8) | 29,863 (27.1) | 7059 (30.9) |
PM2.5 (ug/m3) | ||||
Mean (SD) | 8.77 | 8.88 | 9.24 | 9.34 |
Range | 2.86–19.63 | 2.39–19.83 | 2.19–23.05 | 2.54–18.57 |
Ozone (ppb) | ||||
Mean (SD) | 35.95 | 35.22 | 34.04 | 33.72 |
Range | 24.54–53.65 | 22.30–57.39 | 24.54–54.22 | 25.46–50.81 |