Table 2. Characteristics of Mammography Plus Ultrasonography Examination Cohort and the Matched Sample and Total Population of Women Receiving Screening Mammography Alonea.
| Variable | Mammography Plus Ultrasonography | Mammography Alone (Matched) | Standardized Mean Difference After Matching | Mammography Alone (Overall) | Standardized Mean Difference Before Matching |
|---|---|---|---|---|---|
| Total | 6081 | 30 062 | NA | 113 293 | NA |
| Age, No. (%), yb | |||||
| 30-39 | 506 (8.3) | 1093 (3.6) | 0.20 | 2800 (2.5) | 0.26 |
| 40-49 | 2516 (41.4) | 12 636 (42.0) | −0.01 | 33 114 (29.2) | 0.26 |
| 50-59 | 2052 (33.7) | 10 477 (34.9) | −0.03 | 32 803 (29.0) | 0.10 |
| 60-69 | 745 (12.3) | 4130 (13.7) | −0.04 | 23 034 (20.3) | −0.22 |
| 70-79 | 212 (3.5) | 1326 (4.4) | −0.05 | 13 857 (12.2) | −0.33 |
| ≥80 | 50 (0.8) | 400 (1.3) | −0.05 | 7685 (6.8) | −0.32 |
| Race/ethnicity, No./total No. (%)b | |||||
| White, non-Hispanic | 2626/3308 (79.4) | 13 330/16 628 (80.2) | −0.02 | 46 107/60 661 (76.0) | 0.08 |
| Black, non-Hispanic | 11/3308 (0.3) | 76/16 628 (0.5) | −0.03 | 654/60 661 (1.1) | −0.10 |
| Asian/Pacific Islander | 396/3308 (12.0) | 1800/16 628 (10.8) | 0.04 | 7681/60 661 (12.7) | −0.02 |
| Hispanic | 213/3308 (6.4) | 1106/16 628 (6.7) | −0.01 | 4685/60 661 (7.7) | −0.05 |
| Mixed/other | 62/3308 (1.9) | 316/16 628 (1.9) | 0.00 | 1534/60 661 (2.5) | −0.04 |
| Menopausal status, No. (%)b | |||||
| Premenopausal | 2074 (34.1) | 11 665 (38.8) | −0.10 | 30 869 (27.2) | 0.15 |
| Postmenopausal | 2723 (44.8) | 12 067 (40.1) | 0.10 | 63 224 (55.8) | −0.22 |
| Surgical/other amenorrhea/unknown | 1284 (21.1) | 6330 (21.1) | 0.00 | 19 200 (16.9) | 0.11 |
| First-degree family history of breast cancer, No./total No. (%)b | |||||
| No | 3460/6055 (57.1) | 21 227/29 915 (71.0) | −0.29 | 95 565/112 462 (85.0) | −0.65 |
| Yes | 2595/6055 (42.9) | 8688/29 915 (29.0) | 0.29 | 16 897/112 462 (15.0) | 0.65 |
| Unknown | 26 | 147 | NA | 831 | NA |
| Year of examination, No. (%)b | |||||
| 2005-2006 | 285 (4.7) | 1784 (5.9) | −0.05 | 16 635 (14.7) | −0.34 |
| 2007-2008 | 1284 (21.1) | 6671 (22.2) | −0.03 | 31 164 (27.5) | −0.15 |
| 2009-2010 | 1999 (32.9) | 9894 (32.9) | 0.00 | 32 216 (28.4) | 0.10 |
| 2011-2013 | 2513 (41.3) | 11 713 (39.0) | 0.05 | 33 278 (29.4) | 0.25 |
| Time since last mammogram, No./total No. (%), yb | |||||
| None | 92/5647 (1.6) | 517/27 958 (1.8) | −0.02 | 4386/106 802 (4.1) | −0.15 |
| 1-2 | 5398/5647 (95.6) | 26 493/27 958 (94.8) | 0.04 | 95 293/106 802 (89.2) | 0.24 |
| ≥3 | 157/5647 (2.8) | 948/27 958 (3.4) | −0.03 | 7123/106 802 (6.7) | −0.18 |
| Unknown | 434 | 2104 | NA | 6491 | NA |
| Breast density, No./total No. (%)b | |||||
| Almost entirely fat | 83/5810 (1.4) | 563/28 930 (1.9) | −0.04 | 8226/111 306 (7.4) | −0.30 |
| Scattered | 1410/5810 (24.3) | 9138/28 930 (31.6) | −0.16 | 63 152/111 306 (56.7) | −0.70 |
| Heterogeneously dense | 3543/5810 (61.0) | 17 126/28 930 (59.2) | 0.04 | 37 074/111 306 (33.3) | 0.58 |
| Extremely dense | 774/5810 (13.3) | 2103/28 930 (7.3) | 0.20 | 2854/111 306 (2.6) | 0.40 |
| Unknown | 271 | 1132 | NA | 1987 | NA |
| Prior benign biopsy result, No. (%)b | |||||
| No prior biopsy | 3045 (50.1) | 18 786 (62.5) | −0.25 | 90 745 (80.1) | −0.66 |
| Biopsy, pathology unknown | 1446 (23.8) | 6696 (22.3) | 0.04 | 15 878 (14.0) | 0.25 |
| Nonproliferative disease | 831 (13.7) | 2956 (9.8) | 0.12 | 4320 (3.8) | 0.36 |
| Proliferative without atypia | 620 (10.2) | 1290 (4.3) | 0.23 | 1808 (1.6) | 0.37 |
| Proliferative with atypia | 109 (1.8) | 287 (1.0) | 0.07 | 418 (0.4) | 0.13 |
| Lobular carcinoma in situ | 30 (0.5) | 47 (0.2) | 0.05 | 124 (0.1) | 0.07 |
| BCSC 5-y risk, No./total No. (%) | |||||
| Low (0%-1.00%) | 1196/5392 (22.2) | 8146/27 931 (29.2) | −0.16 | 37 108/97 393 (38.1) | −0.35 |
| Average (1.00%-1.66%) | 1693/5392 (31.4) | 9573/27 931(34.3) | −0.06 | 37 693/97 393 (38.7) | −0.15 |
| Intermediate (1.67%-2.49%) | 1349/5392 (25.0) | 6317/27 931 (22.6) | 0.06 | 16 127/97 393 (16.6) | 0.21 |
| High (2.50%-3.99%) | 976/5392 (18.1) | 3402/27 931 (12.2) | 0.17 | 5760/97 393 (5.9) | 0.38 |
| Very high (≥3.99%) | 178/5392 (3.3) | 493/27 931 (1.8) | 0.10 | 705/97 393 (0.7) | 0.19 |
| Unknown | 689 | 2131 | NA | 15 900 | NA |
Abbreviations: BCSC, Breast Cancer Surveillance Consortium; NA, not applicable.
a
For each variable, missing values were not included when calculating the distributions across categories.
b
Variables controlled for in calculating propensity score.