Table 1.
Selected characteristics of the study population at blood collection (n cases/controls =1558/1558)
| Variables | Cases | Controls |
|---|---|---|
| Mean (SD) or N (%) | Mean (SD) or N (%) | |
| Breast cancer cases characteristics | ||
| Time between blood collection and diagnosis in years | 8.6 (2.8) | – |
| Age at diagnosis in years | 61.4 (8.3) | – |
| ER positive | ||
| Negative | 305 (19.6) | – |
| Positive | 1253 (80.4) | – |
| PR status | ||
| Negative | 509 (31.8) | – |
| Positive | 1104 (68.2) | – |
| HER2 status | ||
| Negative | 1224 (78.6) | – |
| Positive | 334 (21.4) | – |
| Molecular status | ||
| ER+PR±HER2+ | 210 (13.7) | – |
| ER+PR±HER2− | 1043 (68.3) | – |
| ER−PR−HER2− | 160 (10.5) | – |
| ER−PR−HER2+ | 115 (7.5) | – |
| Sociodemographic, lifestyle and reproductive factors | ||
| Age at blood collection in years | 52.5 (7.9) | 52.5 (7.9) |
| Education level (N missing=63) | ||
| Primary/no schooling | 557 (37) | 571 (37) |
| Technical/professional/secondary | 647 (42) | 638 (42) |
| Longer education | 324 (21) | 316 (21) |
| Time since last meal at blood collection in hours (N missing=49) | ||
| < 3 h | 706 (46) | 712 (46) |
| ≥ 3–≤ 6 h | 273 (18) | 272 (18) |
| > 6 h | 552 (36) | 552 (36) |
| Physical activity index (N missing=27) | ||
| Inactive | 349 (23) | 312 (20) |
| Moderately inactive | 573 (37) | 610 (40) |
| Moderately active | 346 (22) | 335 (22) |
| Active | 282 (18) | 282 (18) |
| Smoking status (N missing=25) | ||
| Never | 875 (56) | 875 (56) |
| Former | 351 (23) | 334 (22) |
| Smoker | 319 (22) | 337 (22) |
| Alcohol consumption at recruitment in g/day (N missing=4) | ||
| Non drinker | 223 (14) | 220 (14) |
| > 0–≤ 3 | 459 (29) | 423 (27) |
| > 3–≤ 12 | 454 (29) | 434 (28) |
| > 12–≤ 24 | 256 (16) | 270 (17) |
| > 24 | 166 (11) | 207 (13) |
| Age at first menstrual period in years (N missing=32) | ||
| ≤ 13 | 977 (63) | 961 (62) |
| > 13 | 568 (37) | 578 (38) |
| Number of full-term pregnancies and age at first full-term pregnancy* (N missing=91) | ||
| Nulliparous | 243 (16) | 213 (14) |
| Age <30 (1-2 children) | 714 (47) | 739 (47) |
| Age <30 (≥3 children) | 340 (22) | 385 (25) |
| Age ≥30 | 215 (14) | 176 (11) |
| Ever breastfed among women with full-term pregnancy | ||
| No | 199 (15) | 188 (14) |
| Yes | 1034 (80) | 1,069 (80) |
| Missing | 68 (5) | 77 (6) |
| Use of exogenous hormones at blood collection | 489 (31.4) | 489 (31.4) |
| Ever use of oral contraceptive at baseline (N missing=11) | 939 (50.5) | 919 (49.5) |
| Ever use of menopausal hormone therapy at baseline among postmenopausal women (N missing=5) | 415 (49.7) | 420 (50.3) |
| Menopausal status at blood collection (N missing=0) | ||
| Premenopausal | 413 (26) | 413 (26) |
| Perimenopausal | 307 (20) | 307 (20) |
| Postmenopausal | 838 (54) | 838 (54) |
| Anthropometric factors | ||
| Weight in kg | ||
| Among premenopausal women | 64.5 (10.7) | 64.8 (11.2) |
| Among perimenopausal women | 67.9 (12.3) | 66.8 (10.4) |
| Among postmenopausal women | 69.1 (12.6) | 66.8 (10.9) |
| Height in cm | ||
| Among premenopausal women | 161.9 (6.5) | 162.1 (6.6) |
| Among perimenopausal women | 162.6 (6.6) | 161.8 (6.8) |
| Among postmenopausal women | 162.1 (6.6) | 161.2 (6.5) |
| Body mass index in kg/m2 | ||
| Among premenopausal women | 24.7 (4.2) | 24.7 (4.1) |
| Among perimenopausal women | 25.7 (4.6) | 25.6 (4.0) |
| Among postmenopausal women | 26.3 (4.7) | 25.7 (4.1) |
| Waist circumference in cm (N missing=78) | ||
| Among premenopausal women | 77.8 (10.2) | 78.0 (10.2) |
| Among perimenopausal women | 81.8 (11.3) | 80.3 (11.1) |
| Among postmenopausal women | 83.3 (11.7) | 81.5 (10.2) |
| Hip circumference in cm (N missing= 78) | ||
| Among premenopausal women | 99.4 (8.2) | 99.9 (8.4) |
| Among perimenopausal women | 102.0 (9.1) | 101.3 (8.3) |
| Among postmenopausal women | 103.3 (9.5) | 101.3 (8.0) |
| Waist to hip ratio (N missing= 78) | ||
| Among premenopausal women | 0.78 (0.06) | 0.78 (0.06) |
| Among perimenopausal women | 0.80 (0.07) | 0.79 (0.09) |
| Among postmenopausal women | 0.81 (0.07) | 0.80 (0.07) |
| Comorbidities | ||
| History of diabetes (N missing=60) | 40 (3) | 22 (1) |
| History of hypertension | ||
| No | 1078 (35) | 1094 (35) |
| Yes | 354 (11) | 323 (10) |
| Missing | 126 (4) | 141 (5) |
Abbreviations: ER, oestrogen receptor; HER2, human epidermal growth factor 2; PR, progesterone receptor; SD, standard deviation.
Note: Controls were matched to cases on the centre of recruitment, age, menopausal status at blood collection, phase of the menstrual cycle for premenopausal women, use of exogenous hormone at blood collection, time of the day, and fasting status at blood collection