Table 1.
Age-adjusted characteristics a of cases and controls in the study by the time between the mammogram and reference date b.
| Characteristic | Cases | Controls | ||||||
|---|---|---|---|---|---|---|---|---|
|
| ||||||||
| Time since the mammogram, years | Time since the mammogram, years | |||||||
|
| ||||||||
| <2 (n=220) | 2–<5 (n=317) | 5–<10 (n=361) | ≥10 (n=130) | <2 (n=481) | 2–<5 (n=513) | 5–<10 (n=571) | ≥10 (n=215) | |
| Mean (SD) | ||||||||
| Percent breast density | 29.2 (17.8) | 30.0 (19.8) | 30.8 (18.5) | 32.7 (16.5) | 22.4 (16.2) | 22.9 (16.7) | 24.2 (18.1) | 26.2 (14.5) |
| Absolute dense area, cm2 | 48.2 (35.6) | 45.0 (31.2) | 50.9 (39.8) | 72.5 (45.7) | 36.6 (29.0) | 37.6 (29.7) | 39.8 (32.7) | 58.8 (36.9) |
| Non-dense area, cm2 | 135 (89) | 132 (91) | 130 (82) | 163 (87) | 152 (87.0) | 149 (88.0) | 148 (98.0) | 187 (94.0) |
| Age, yearsc | 63.2 (6.9) | 63.5 (6.6) | 66.0 (5.9) | 69.1 (6.6) | 62.8 (6.8) | 63.3 (6.1) | 66.0 (6.3) | 69.6 (6.1) |
| Age at menarche, y | 12.7 (2.1) | 12.5 (1.4) | 12.5 (1.3) | 12.5 (1.5) | 12.6 (1.5) | 12.6 (1.4) | 12.7 (1.3) | 12.4 (1.2) |
| Age at natural menopause, y | 49.4 (5.2) | 50.1 (3.7) | 49.1 (4.4) | 50.2 (3.9) | 49.4 (5.2) | 50.1 (3.7) | 49.1 (4.4) | 50.2 (3.9) |
| BMI, kg/m2 | 26.4 (5.4) | 26.6 (4.9) | 26.3 (4.6) | 26.2 (4.1) | 26.1 (5.1) | 26.3 (5.2) | 26.6 (4.6) | 26.4 (4.6) |
| Alcohol use, g/day | 6.2 (8.7) | 4.1 (7.6) | 6.3 (10.3) | 4.5 (8.2) | 5.5 (9.3) | 5.5 (9.3) | 5.2 (8.8) | 5.3 (7.7) |
| Percentages | ||||||||
| Parity and age at first child’s birth | ||||||||
| Nulliparous | 10 | 6 | 7 | 11 | 7 | 6 | 5 | 5 |
| 1–4 children, age at first birth <25 yrs | 32 | 31 | 41 | 43 | 30 | 36 | 40 | 47 |
| 1–4 children, age at first birth 25–29 yrs | 32 | 35 | 31 | 27 | 33 | 33 | 30 | 24 |
| 1–4 children, age at first birth ≥ 30 yrs | 8 | 11 | 9 | 7 | 9 | 7 | 9 | 9 |
| ≥ 5 children, age at first birth <25 yrs | 12 | 9 | 7 | 9 | 13 | 10 | 12 | 10 |
| ≥ 5 children, age at first birth ≥ 25 yrs | 7 | 8 | 5 | 3 | 7 | 8 | 5 | 5 |
| PMH use | ||||||||
| Never used hormones | 27 | 21 | 17 | 12 | 32 | 28 | 22 | 17 |
| Current hormone use | 46 | 54 | 65 | 67 | 42 | 43 | 51 | 55 |
| Past hormone use | 24 | 20 | 14 | 19 | 23 | 25 | 25 | 25 |
| Unknown status of hormone use | 3 | 5 | 4 | 2 | 3 | 4 | 2 | 3 |
| Family history of breast cancerd | 11 | 19 | 21 | 22 | 14 | 14 | 15 | 14 |
| Personal history of benign breast disease | 26 | 33 | 34 | 43 | 25 | 25 | 28 | 31 |
| Smoking status (ever) | 55 | 55 | 57 | 52 | 53 | 47 | 54 | 57 |
Abbreviations: SD = standard deviation, BMI = body mass index, PMH = postmenopausal hormone.
a
At the reference date
b
The reference date is the date of diagnosis for case and its matched control
c
Values are not adjusted
d
First-degree relative with breast cancer diagnosis.