Table 1.
Characteristics of study participants
| Screen-detected cases | Interval cases | ||||||
|---|---|---|---|---|---|---|---|
| Cases (n = 244) | Controls (n = 700) | P | Cases (n = 148) | Controls (n = 446) | P | P a | |
| Age at baseline, years | 56 (8) | 56 (8) | 0.72 | 54 (8) | 54 (8) | 0.72 | 0.01 |
| Age at mammogram, years | 59 (7) | 59 (7) | 0.82 | 57 (7) | 57 (7) | 0.79 | <0.01 |
| Age at diagnosis, years | 65 (7) | 62 (7) | <0.001 | ||||
| Time between age at mammogram and reference age, years | 6 (3) | 6 (3) | 0.58 | 5 (3) | 5 (4) | 0.93 | 0.12 |
| Total energy intake, MJ/day | 8.4 (2.9) | 8.6 (3.5) | 0.40 | 8.7 (3.2) | 8.7 (3.1) | 0.91 | 0.30 |
| BMI, kg/m2 | |||||||
| All women | 27.5 (4.9) | 26.7 (4.9) | 0.04 | 26.7 (5.3) | 26.5 (4.8) | 0.68 | 0.11 |
| Premenopausal | 27.2 (5.7) | 26.2 (5.0) | 0.17 | 25.9 (4.9) | 26.1 (4.6) | 0.72 | 0.15 |
| Postmenopausal | 27.6 (4.6) | 27.0 (4.9) | 0.10 | 27.2 (5.5) | 26.7 (5.0) | 0.41 | 0.51 |
| BMI at age 18–21 years, kg/m2 | 21.5 (2.9) | 21.5 (2.9) | 0.86 | 21.4 (2.5) | 21.5 (2.8) | 0.54 | 0.66 |
| Breast | |||||||
| Total area, cm2 | 143.7 (60.9) | 137.8 (57.6) | 0.17 | 125.0 (56.9) | 133.4 (60.3) | 0.14 | <0.01 |
| Non-dense area, cm2 | 124.2 (62.1) | 120.9 (58.8) | 0.47 | 96.5 (55.6) | 115.3 (60.6) | <0.001 | <0.0001 |
| Dense area, cm2 | 19.6 (21.7) | 16.8 (20.6) | 0.08 | 28.5 (24.5) | 18.1 (19.4) | <0.0001 | <0.001 |
| Percent dense area | 15.5 (15.7) | 14.0 (15.3) | 0.18 | 25.2 (17.9) | 15.4 (14.7) | <0.0001 | <0.0001 |
| Country of birth, n (%) | |||||||
| Anglo Saxon/other | 204 (84) | 583 (83) | 0.99 | 123 (83) | 371 (83) | 0.99 | 0.70 |
| Italy | 25 (10) | 74 (11) | 13 (9) | 40 (9) | |||
| Greece | 15 (6) | 43 (6) | 12 (8) | 35 (8) | |||
| Age at menarche, years n (%) | |||||||
| <12 | 47 (19) | 125 (18) | 0.92 | 31 (21) | 75 (17) | 0.69 | 0.74 |
| 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, n (%), | |||||||
| Nulliparous | 38 (16) | 84 (12) | 0.03 | 25 (17) | 62 (14) | 0.63 | 0.22 |
| Parous, never lactated | 10 (4) | 61 (9) | 12 (8) | 34 (8) | |||
| Parous, lactated | 190 (78) | 542 (77) | 108 (73) | 343 (77) | |||
| Menopausal status n (%) | |||||||
| Premenopausal | 69 (28) | 195 (28) | 0.88 | 59 (40) | 170 (38) | 0.72 | 0.02 |
| Postmenopausal | 174 (71) | 504 (72) | 89 (60) | 275 (62) | |||
| Hormone replacement therapy use, n (%) | |||||||
| Never | 169 (69) | 493 (70) | 0.75 | 98 (66) | 323 (72) | 0.17 | 0.55 |
| Ever | 74 (30) | 205 (29) | 49 (33) | 122 (27) | |||
| Oral contraceptive use, n (%) | |||||||
| Never | 93 (38) | 283 (40) | 0.53 | 58 (39) | 157 (35) | 0.4 | 0.86 |
| Ever | 150 (61) | 415 (59) | 90 (61) | 287 (64) | |||
| Alcohol consumption, n (%) | |||||||
| Lifetime abstainers | 109 (45) | 257 (37) | 0.10 | 43 (29) | 160 (36) | 0.3 | <0.01 |
| 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 cancerb, n (%) | |||||||
| No | 185 (76) | 548 (78) | 0.08 | 101 (68) | 341 (76) | <0.001 | 0.18 |
| Yes | 38 (16) | 77 (11) | 30 (20) | 43 (10) | |||
| ER, n (%) | |||||||
| Positive | 188 (77.0) | 94 (63.5) | <0.01 | ||||
| Negative | 45 (18.4) | 45 (30.4) | |||||
| PR, n (%) | |||||||
| Positive | 126 (51.6) | 57 (38.5) | 0.02 | ||||
| Negative | 106 (43.4) | 80 (54.1) | |||||
| HER2, n (%) | |||||||
| Positive | 73 (29.9) | 41 (27.7) | 0.64 | ||||
| Negative | 153 (62.7) | 96 (64.9) | |||||
| Grade n (%) | |||||||
| Well-differentiated | 62 (25.4) | 24 (16.2) | <0.01 | ||||
| Moderately differentiated | 104 (42.6) | 52 (35.1) | |||||
| Poorly differentiated | 65 (26.6) | 61 (41.2) | |||||
| Nodal status, n (%) | |||||||
| Positive | 39 (16.0) | 65 (43.9) | <0.001 | ||||
| Negative | 190 (77.9) | 71 (48.0) | |||||
| Tumor size, n (%) | |||||||
| <1 cm | 76 (31.1) | 25 (16.9) | <0.001 | ||||
| 1–2 cm | 116 (47.5) | 51 (34.5) | |||||
| ≥2 cm | 49 (20.1) | 65 (43.9) | |||||
Results are presented as mean (SD) unless stated otherwise. P values are for Pearson’s χ2 test or Fisher’s exact test for categorical variables and Student’s two-sided t test for continuous variables. a P values are for tests comparing screen-detected cases with interval cases. bFamily history of breast cancer is defined as having any relative with breast cancer. BMI body mass index, SD standard deviation, ER estrogen receptor, PR progesterone receptor, HER2 human epidermal growth factor receptor-2