Table 1.
Distribution of risk factors and age-adjusted ORs and 95% CIs, postmenopausal breast cancer, Montreal, Canada (n = 799).
| Variable (reference category)a | Cases [n (%)] | Controls [n (%)] | OR (95% CI) |
|---|---|---|---|
| Mother or sister with breast cancer (no) | 210 (54.8) | 279 (67.1) | 1 |
| Yes | 83 (21.7) | 47 (11.3) | 2.36 (1.58–3.52) |
| No for mother, no sisters | 79 (20.6) | 76 (18.3) | 1.40 (0.97–2.01) |
| Missing information | 11 (2.9) | 14 (3.4) | 1.13 (0.50–2.55) |
| Oophorectomy (never) | 276 (72.1) | 194 (46.6) | 1 |
| Only one ovary removed | 27 (7) | 30 (7.2) | 0.61 (0.35–1.07) |
| Age at bilateral oophorectomy, years | |||
| < 44 | 26 (6.8) | 34 (8.2) | 0.55 (0.32–0.95) |
| 45–49 | 19 (5) | 15 (3.6) | 0.89 (0.44–1.79) |
| 50–54 | 16 (4.2) | 26 (6.3) | 0.39 (0.20–0.76) |
| ≥ 55 | 17 (4.4) | 106 (25.5) | 0.12 (0.07–0.20) |
| Missing information | 2 (0.5) | 11 (2.6) | 0.13 (0.03–0.59) |
| Education, years (≤ 7) | 107 (27.9) | 154 (37) | 1 |
| 8–10 | 78 (20.4) | 107 (25.7) | 1.05 (0.72–1.54) |
| 11–17 | 178 (46.5) | 138 (33.2) | 1.82 (1.30–2.53) |
| ≥ 18 | 20 (5.2) | 17 (4.1) | 1.58 (0.78–3.17) |
| Ethnicity (French) | 232 (60.6) | 219 (52.6) | 1 |
| English and others | 98 (25.6) | 110 (26.4) | 0.86 (0.62–1.20) |
| Jewish and Italian | 53 (13.8) | 87 (20.9) | 0.58 (0.39–0.86) |
| Age at menarche, years (≥ 16) | 24 (6.3) | 39 (9.4) | 1 |
| 14–15 | 97 (25.3) | 109 (26.2) | 1.47 (0.82–2.62) |
| 13 | 110 (28.7) | 100 (24) | 1.82 (1.02–3.24) |
| 12 | 78 (20.4) | 98 (23.6) | 1.28 (0.71–2.30) |
| ≤ 11 | 74 (19.3) | 70 (16.8) | 1.65 (0.90–3.02) |
| Age at first full-term pregnancy, years (never) | 83 (21.7) | 77 (18.5) | 1 |
| < 18 | 15 (3.9) | 12 (2.9) | 1.12 (0.49–2.55) |
| ≥ 18 to 26 | 166 (43.3) | 214 (51.4) | 0.71 (0.49–1.04) |
| > 26 to 30 | 59 (15.4) | 56 (13.5) | 1.00 (0.62–1.62) |
| > 30 | 46 (12) | 36 (8.7) | 1.24 (0.72–2.12) |
| Pregnant but never full term | 14 (3.7) | 21 (5) | 0.59 (0.28–1.24) |
| Breast-feeding, duration, weeks (0) | 296 (77.3) | 303 (72.8) | 1 |
| 0–80 | 69 (18) | 77 (18.5) | 0.93 (0.65–1.34) |
| > 80 | 18 (4.7) | 36 (8.7) | 0.53 (0.30–0.96) |
| Years of oral contraception use (never) | 248 (64.8) | 290 (69.7) | 1 |
| < 1 | 42 (11) | 25 (6) | 1.78 (1.04–3.05) |
| ≥ 1 | 93 (24.3) | 101 (24.3) | 0.96 (0.67–1.38) |
| Hormone replacement therapy, months (0) | 170 (44.4) | 236 (56.7) | 1 |
| 1–19 | 53 (13.8) | 57 (13.7) | 1.28 (0.84–1.95) |
| 20–44 | 29 (7.6) | 34 (8.2) | 1.14 (0.67–1.96) |
| 45–74 | 35 (9.1) | 21 (5) | 2.19 (1.23–3.92) |
| 75–99 | 16 (4.2) | 13 (3.1) | 1.58 (0.73–3.39) |
| ≥ 100 | 80 (20.9) | 55 (13.2) | 1.98 (1.33–2.95) |
| Body mass index (18.5 to < 25) | 190 (49.6) | 194 (46.6) | 1 |
| 25 to < 30 | 123 (32.1) | 133 (32.0) | 0.97 (0.71–1.34) |
| > 30 to < 35 | 48 (12.5) | 51 (12.3) | 1.00 (0.64–1.56) |
| ≥ 35 | 15 (3.9) | 28 (6.7) | 0.54 (0.28–1.06) |
| < 18.5 | 6 (1.6) | 9 (2.2) | 0.69 (0.24–1.99) |
| Missing information | 1 (0.3) | 1 (0.2) | NE |
| Tobacco exposure (none)b | 45 (11.7) | 52 (12.5) | 1 |
| Environmental tobacco smoke only | 160 (41.8) | 148 (35.6) | 1.17 (0.66–2.08) |
| Active smoker with or without exposure to environmental tobacco smoke | 176 (46) | 209 (50.2) | 1.02 (0.65–1.61) |
| Missing information | 2 (0.5) | 7 (1.7) | NE |
| Respondent (self) | 362 (94.5) | 362 (87) | 1 |
| Proxy | 21 (5.5) | 54 (13) | 0.41 (0.24–0.69) |
| Alcohol status (never drinker)c | 193 (50.4) | 229 (55) | 1 |
| Former drinker | 50 (13.1) | 55 (13.2) | 1.01 (0.66–1.57) |
| Infrequent drinker | 53 (13.8) | 53 (12.7) | 1.15 (0.75–1.76) |
| Current drinker | 87 (22.7) | 79 (19) | 1.26 (0.88–1.81) |
| Benign breast disease (no) | 197 (51.4) | 333 (80) | 1 |
| Yes | 185 (48.3) | 83 (20) | 3.71 (2.70–5.08) |
| Missing information | 1 (0.3) | 0 (0) | NE |
| Occupational exposure to solvents with reactive metabolites (not exposed)d | 338 (88.3) | 374 (89.9) | 1 |
| Nonsubstantial, 5 years | 5 (1.3) | 4 (1) | 1.35 (0.36–5.09) |
| Substantial, 5 years | 6 (1.6) | 5 (1.2) | 1.26 (0.38–4.17) |
| Exposed only at R = 1 | 12 (3.1) | 9 (2.2) | 1.43 (0.60–3.45) |
| Other exposures | 22 (5.7) | 24 (5.8) | 0.99 (0.55–1.81) |
| Occupational exposure to extremely low magnetic fields (not exposed)d | 81 (21.1) | 102 (24.5) | 1 |
| Nonsubstantial, 5 years | 107 (27.9) | 96 (23.1) | 1.30 (0.86–1.97) |
| Substantial, 5 years | 48 (12.5) | 44 (10.6) | 1.30 (0.78–2.17) |
| Exposed only at R = 1 | 8 (2.1) | 18 (4.3) | 0.57 (0.24–1.37) |
| Other exposures | 139 (36.3) | 156 (37.5) | 1.06 (0.73–1.55) |
| Occupational exposure to carbon monoxide (not exposed)d | 299 (78.1) | 339 (81.5) | 1 |
| Nonsubstantial, 5 years | 36 (9.4) | 21 (5.0) | 1.87 (1.07–3.27) |
| Substantial, 5 years | 0 (0.0) | 0 (0.0) | NE |
| Exposed only at R = 1 | 1 (0.3) | 1 (0.2) | 1.18 (0.07–19.10) |
| Other exposures | 47 (12.3) | 55 (13.2) | 0.94 (0.62–1.43) |
| Occupational exposure to polycyclic aromatic hydrocarbons from petroleum (not exposed)d | 354 (92.4) | 386 (92.8) | 1 |
| Nonsubstantial, 5 years | 9 (2.3) | 4 (1.0) | 2.34 (0.72–7.63) |
| Substantial, 5 years | 2 (0.5) | 2 (0.5) | 1.07 (0.15–7.69) |
| Exposed only at R = 1 | 2 (0.5) | 8 (1.9) | 0.28 (0.64–1.22) |
| Other exposures | 16 (4.2) | 16 (3.8) | 1.03 (0.51–2.10) |
NE, not estimated.
Categories shown are those modeled in the analyses (see Table 3); reference group for each category is in parentheses.
This variable was compiled with information acquired from several questions. Subjects were asked if they had smoked 100 cigarettes over the course of their lifetime, along with follow-up questions, to determine whether they were former, current, or never-smokers. Subjects were also asked whether they had ever been exposed to residential or occupational environmental tobacco smoke, along with follow-up questions concerning duration and kind of exposure.
The categories for this variable were determined based on information from several questions. Subjects were asked whether there had ever been a time in their life when they had consumed one or more drinks of beer, wine, or liquor (respectively) on a monthly basis, or on a weekly basis.
Substantial exposure, ≥ 5 years of exposure at medium or high levels of intensity; nonsubstantial exposure, < 5 years of exposure at medium or high levels of intensity, but still ≥ 5 years of exposure at any intensity; exposed only at R = 1, exposure only at the lowest level of confidence; other exposures, exposures totaling < 5 years.