Table 1.
Characteristics of study participants
| Screen-detected cases | Controls | Interval cases | Controls | |
|---|---|---|---|---|
| (N = 244) | (N = 700) | (N = 148) | (N = 446) | |
| Mean (SD) | Mean (SD) | Mean (SD) | Mean (SD) | |
| Age at baseline, years | 56 (8) | 56 (8) | 54 (8) | 54 (8) |
| Age at mammogram, years | 59 (7) | 59 (7) | 57 (7) | 57 (7) |
| Age at diagnosis, years | 65 (7) | 62 (7) | ||
| Time between age at mammogram and reference age, years | 6 (3) | 6 (3) | 5 (3) | 5 (4) |
| Total energy intake, MJ/day | 8.4 (2.9) | 8.6 (3.5) | 8.7 (3.2) | 8.7 (3.1) |
| BMI, kg/m2 | ||||
| All women | 27.5 (4.9) | 26.7 (4.9) | 26.7 (5.3) | 26.5 (4.8) |
| Premenopausal | 27.2 (5.7) | 26.2 (5.0) | 25.9 (4.9) | 26.1 (4.6) |
| Postmenopausal | 27.6 (4.6) | 27.0 (4.9) | 27.2 (5.5) | 26.7 (5.0) |
| BMI at age 18–21 years, kg/m2 | 21.5 (2.9) | 21.5 (2.9) | 21.4 (2.5) | 21.5 (2.8) |
| Breast | ||||
| Total area, cm2 | 143.7 (60.9) | 137.8 (57.6) | 125.0 (56.9) | 133.4 (60.3) |
| Non-dense area, cm2 | 124.2 (62.1) | 120.9 (58.8) | 96.5 (55.6) | 115.3 (60.6) |
| Dense area, cm2 | 19.6 (21.7) | 16.8 (20.6) | 28.5 (24.5) | 18.1 (19.4) |
| Percent mammographic density, % | 15.5 (15.7) | 14.0 (15.3) | 25.2 (17.9) | 15.4 (14.7) |
| Country of birth | N (%) | N (%) | N (%) | N (%) |
| Anglo Saxon/ Other | 204 (84) | 583 (83) | 123 (83) | 371 (83) |
| Italy | 25 (10) | 74 (11) | 13 (9) | 40 (9) |
| Greece | 15 (6) | 43 (6) | 12 (8) | 35 (8) |
| Age at menarche, years | ||||
| < 12 | 47 (19) | 125 (18) | 31 (21) | 75 (17) |
| 12 | 52 (21) | 145 (21) | 25 (17) | 86 (19) |
| 13 | 55 (23) | 169 (24) | 36 (24) | 111 (25) |
| 14+ | 88 (36) | 261 (37) | 56 (38) | 174 (39) |
| Parity and lactation | ||||
| Nulliparous | 38 (16) | 84 (12) | 25 (17) | 62 (14) |
| Parous, never lactated | 10 (4) | 61 (9) | 12 (8) | 34 (8) |
| Parous, lactated | 190 (78) | 542 (77) | 108 (73) | 343 (77) |
| Menopausal status | ||||
| Premenopausal | 69 (28) | 195 (28) | 59 (40) | 170 (38) |
| Postmenopausal | 174 (71) | 504 (72) | 89 (60) | 275 (62) |
| Hormone replacement therapy use | ||||
| Never | 169 (69) | 493 (70) | 98 (66) | 323 (72) |
| Ever | 74 (30) | 205 (29) | 49 (33) | 122 (27) |
| Oral contraceptive use | ||||
| Never | 93 (38) | 283 (40) | 58 (39) | 157 (35) |
| Ever | 150 (61) | 415 (59) | 90 (61) | 287 (64) |
| Alcohol consumption | ||||
| Lifetime abstainers | 109 (45) | 257 (37) | 43 (29) | 160 (36) |
| Ex-drinkers | 13 (5) | 24 (3) | 3 (2) | 13 (3) |
| Low intake, 1–19 g/day | 97 (40) | 337 (48) | 78 (53) | 223 (50) |
| Medium intake, 20–39 g/day | 19 (8) | 61 (9) | 20 (14) | 38 (9) |
| High intake, ≥ 40 g/day | 6 (2) | 21 (3) | 4 (3) | 12 (3) |
| Family history of breast cancera | ||||
| No | 185 (76) | 548 (78) | 101 (68) | 341 (76) |
| Yes | 38 (16) | 77 (11) | 30 (20) | 43 (10) |
| ER | ||||
| Positive | 188 (77.0) | 94 (63.5) | ||
| Negative | 45 (18.4) | 45 (30.4) | ||
| PR | ||||
| Positive | 126 (51.6) | 57 (38.5) | ||
| Negative | 106 (43.4) | 80 (54.1) | ||
| HER2 | ||||
| Positive | 73 (29.9) | 41 (27.7) | ||
| Negative | 153 (62.7) | 96 (64.9) | ||
| Grade | ||||
| Well differentiated | 62 (25.4) | 24 (16.2) | ||
| Moderately differentiated | 104 (42.6) | 52 (35.1) | ||
| Poorly differentiated | 65 (26.6) | 61 (41.2) | ||
| Size | ||||
| < 1 cm | 76 (31.1) | 25 (16.9) | ||
| 1–2 cm | 116 (47.5) | 51 (34.5) | ||
| ≥ 2 cm | 49 (20.1) | 65 (43.9) | ||
| Nodal Status | ||||
| Positive | 39 (16.0) | 65 (43.9) | ||
| Negative | 190 (77.9) | 71 (48.0) | ||
Abbreviations: BMI body mass index, SD standard deviation
aFamily history of breast cancer is defined as having any relative with breast cancer