Table 3.
Associations with breast cancer risk for demographic, reproductive and other risk factors based on a comparison of cases and population controls, Australia 1992–99, Ontario 1996–98 and San Francisco 1995–98
| Population controls, n (%) | Cases, n (%) | Adjusteda OR (95% CI) | P-value | Adjustedb OR (95% CI) | P-value | |
|---|---|---|---|---|---|---|
| Education | ||||||
| Partial or no secondary | 787 (27) | 1124 (31) | 1 | 1 | ||
| Secondary completed | 1272 (44) | 1535 (42) | 0.69 (0.61–0.79) | <0.001 | 0.67 (0.59–0.77) | <0.001 |
| University degree | 815 (28) | 968 (27) | 0.67 (0.58–0.78) | <0.001 | 0.62 (0.54–0.72) | <0.001 |
| P-trend | <0.001 | <0.001 | ||||
| Foreign bornc | ||||||
| No | 2330 (81) | 2788 (77) | 1 | 1 | ||
| Yes | 542 (19) | 844 (23) | 1.31 (1.16–1.50) | <0.001 | 1.40 (1.22–1.60) | <0.001 |
| Marital status | ||||||
| Ever married | 2585 (90) | 3324 (91) | 1 | 1 | ||
| Never married | 287 (10) | 317 (9) | 0.87 (0.73–1.05) | 0.1 | 0.67 (0.54–0.83) | <0.001 |
| Age at menarche (years) | ||||||
| <12 | 578 (20) | 705 (20) | 1 | 1 | ||
| 12 | 677 (24) | 894 (25) | 1.12 (0.96–1.31) | 0.2 | 1.15 (0.98–1.35) | 0.09 |
| 13 | 881 (31) | 1,101 (30) | 1.04 (0.90–1.21) | 0.6 | 1.05 (0.90–1.23) | 0.5 |
| ≥14 | 726 (25) | 916 (25) | 1.02 (0.87–1.19) | 0.8 | 1.05 (0.89–1.23) | 0.6 |
| Trend (per year) | 0.99 (0.95–1.02) | 0.4 | 0.99 (0.96–1.02) | 0.6 | ||
| Ever parous | ||||||
| No | 588 (20) | 820 (23) | 1 | 1 | ||
| Yes | 2,289 (80) | 2,823 (77) | 0.73 (0.62–0.84) | <0.001 | 0.73 (0.62–0.85) | <0.001 |
| Parous women | ||||||
| Number of births | ||||||
| 1 | 419 (18) | 506 (18) | 1 | 1 | ||
| 2 | 1,022 (45) | 1,325 (47) | 1.05 (0.89–1.24) | 0.6 | 1.03 (0.87–1.23) | 0.7 |
| 3 | 563 (25) | 679 (24) | 1.03 (0.85–1.24) | 0.8 | 1.02 (0.84–1.24) | 0.8 |
| ≥4 | 285 (12) | 313 (11) | 0.95 (0.75–1.19) | 0.6 | 0.92 (0.72–1.16) | 0.5 |
| Trend (per birth) | 1.00 (0.94–1.06) | 0.9 | 1.00 (0.94–1.06) | 0.9 | ||
| Age at first birth (years) | ||||||
| <20 | 305 (13) | 361 (13) | 0.95 (0.79–1.15) | 0.6 | 0.96 (0.79–1.17) | 0.7 |
| 20–24 | 829 (36) | 990 (35) | 1 | 1 | ||
| 25–29 | 735 (32) | 968 (34) | 1.14 (0.98–1.31) | 0.08 | 1.14 (0.98–1.32) | 0.09 |
| ≥30 | 418 (18) | 501 (18) | 1.02 (0.86–1.22) | 0.8 | 1.04 (0.86–1.26) | 0.7 |
| Trend (per 5 years) | 1.04 (0.97–1.11) | 0.3 | 1.04 (0.97–1.12) | 0.2 | ||
| Years since last birth | ||||||
| <10 | 664 (29) | 910 (32) | 1 | 1 | ||
| 10–19 | 608 (27) | 750 (27) | 1.06 (0.86–1.30) | 0.6 | 1.03 (0.83–1.27) | 0.8 |
| 20–29 | 606 (27) | 818 (29) | 1.30 (0.99–1.69) | 0.06 | 1.26 (0.96–1.67) | 0.1 |
| ≥30 | 409 (18) | 342 (12) | 0.81 (0.57–1.15) | 0.2 | 0.81 (0.55–1.17) | 0.3 |
| Trend (per 10 years) | 0.94 (0.84–1.07) | 0.4 | 0.93 (0.82–1.06) | 0.3 | ||
| Lifetime breastfeeding (months) | ||||||
| 0 | 726 (32) | 922 (33) | 1 | 1 | ||
| 1–6 | 545 (24) | 723 (26) | 0.97 (0.82–1.13) | 0.7 | 0.96 (0.81–1.13) | 0.6 |
| 7–18 | 590 (26) | 710 (25) | 0.80 (0.68–0.94) | 0.008 | 0.77 (0.65–0.91) | 0.002 |
| >18 | 424 (19) | 446 (16) | 0.66 (0.55–0.79) | <0.001 | 0.62 (0.51–0.76) | <0.001 |
| Trend (per 6 months) | 0.93 (0.91–0.96) | <0.001 | 0.92 (0.89–0.95) | <0.001 | ||
| Age at menopause (years) | ||||||
| <50 | 405 (57) | 452 (51) | 1 | 1 | ||
| ≥50 | 305 (43) | 437 (49) | 1.61 (1.27–2.04) | <0.001 | 1.62 (1.26–2.09) | <0.001 |
| Trend (per 5 years) | 1.30 (1.17–1.45) | <0.001 | 1.29 (1.15–1.44) | <0.001 | ||
| Height (cm) | ||||||
| ≤158 | 735 (26) | 851 (24) | 1 | 1 | ||
| 159–163 | 765 (27) | 955 (27) | 1.17 (1.01–1.35) | 0.03 | 1.20 (1.03–1.39) | 0.02 |
| 164–168 | 729 (25) | 967 (27) | 1.24 (1.08–1.44) | 0.003 | 1.25 (1.07–1.45) | 0.004 |
| ≥ 169 | 635 (22) | 824 (23) | 1.24 (1.07–1.45) | 0.005 | 1.25 (1.07–1.47) | 0.006 |
| Trend (per 10 cm) | 1.17 (1.08–1.26) | <0.001 | 1.16 (1.07–1.26) | <0.001 |
aAdjusted for age (5-year categories) by study, educational attainment by study, country of birth and marital status, where applicable.
bAdjusted for age (5-year categories) by study, educational attainment by study, country of birth, marital status, ever parous, number of births, age at menarche and family history of breast cancer, where applicable.
cBorn outside the country in which the corresponding study was conducted.