Selected reproductive characteristics of breast cancer cases and control women, Shanghai, China
| Characteristic . | Cases, n = 378 (age-adjusted %)* . | Controls, n = 1,070 (%) . | ||
|---|---|---|---|---|
| Age at menarche | ||||
| ≤13 | 66 (19.9) | 171 (15.6) | ||
| 14 | 69 (19.9) | 204 (19.1) | ||
| 15 | 91 (23.2) | 215 (20.1) | ||
| 16 | 68 (16.8) | 221 (20.7) | ||
| ≥17 | 84 (20.1) | 257 (24.0) | ||
| No. live births | ||||
| 0 | 21 (5.4) | 41 (3.8) | ||
| 1 | 193 (63.6) | 713 (66.6) | ||
| 2 | 66 (13.4) | 124 (11.6) | ||
| >3 | 97 (17.4) | 188 (17.6) | ||
| Missing | 1 (0.2) | 4 (0.4) | ||
| Age at 1st live birth (y) | ||||
| No live birth | 21 (5.4) | 41 (3.8) | ||
| ≤24 | 118 (21.9) | 275 (25.7) | ||
| 25-29 | 170 (52.4) | 599 (56.0) | ||
| ≥30 | 65 (19.5) | 151 (14.1) | ||
| Missing | 4 (0.8) | 4 (0.4) | ||
| Duration of breast-feeding†(mos) | ||||
| Never | 73 (21.5) | 233 (21.8) | ||
| ≤6 | 69 (20.0) | 209 (19.5) | ||
| 7-12 | 104 (32.5) | 361 (33.7) | ||
| 13-24 | 55 (11.6) | 115 (10.8) | ||
| ≥25 | 77 (13.9) | 152 (14.2) | ||
| Duration of oral contraceptive use (y) | ||||
| Never used | 332 (89.0) | 978 (91.4) | ||
| ≤1 | 21 (5.8) | 35 (3.3) | ||
| ≥1 | 25 (5.3) | 56 (5.2) | ||
| Induced abortions | ||||
| 0 | 163 (40.7) | 437 (40.8) | ||
| 1 | 138 (37.1) | 427 (39.9) | ||
| ≥2 | 56 (16.8) | 167 (15.6) | ||
| Missing | 21 (5.4) | 39 (3.7) | ||
| Years since last induced abortion† | ||||
| None | 163 (40.7) | 437 (40.8) | ||
| 0-10 | 41 (14.6) | 129 (12.1) | ||
| 11-15 | 49 (16.7) | 185 (17.3) | ||
| 16-20 | 29 (7.6) | 120 (11.2) | ||
| >20 | 54 (10.1) | 145 (13.6) | ||
| Missing years | 42 (10.3) | 54 (5.1) | ||
| No. prior benign breast lumps | ||||
| 0 | 360 (94.5) | 1,038 (97.0) | ||
| 1 | 13 (3.9) | 22 (2.1) | ||
| ≥2 | 5 (1.6) | 10 (0.9) | ||
| Times breast self-examination/y‡ | ||||
| 0 | 198 (50.8) | 725 (67.8) | ||
| 1-6 | 80 (21.4) | 137 (12.8) | ||
| 7-12 | 85 (23.8) | 198 (18.5) | ||
| ≥13 | 10 (3.1) | 7 (0.7) | ||
| Missing | 5 (0.9) | 3 (0.2) | ||
| Menopause | ||||
| No | 187 (62.7) | 687 (64.2) | ||
| Yes | 191 (37.3) | 383 (35.8) | ||
| Characteristic . | Cases, n = 378 (age-adjusted %)* . | Controls, n = 1,070 (%) . | ||
|---|---|---|---|---|
| Age at menarche | ||||
| ≤13 | 66 (19.9) | 171 (15.6) | ||
| 14 | 69 (19.9) | 204 (19.1) | ||
| 15 | 91 (23.2) | 215 (20.1) | ||
| 16 | 68 (16.8) | 221 (20.7) | ||
| ≥17 | 84 (20.1) | 257 (24.0) | ||
| No. live births | ||||
| 0 | 21 (5.4) | 41 (3.8) | ||
| 1 | 193 (63.6) | 713 (66.6) | ||
| 2 | 66 (13.4) | 124 (11.6) | ||
| >3 | 97 (17.4) | 188 (17.6) | ||
| Missing | 1 (0.2) | 4 (0.4) | ||
| Age at 1st live birth (y) | ||||
| No live birth | 21 (5.4) | 41 (3.8) | ||
| ≤24 | 118 (21.9) | 275 (25.7) | ||
| 25-29 | 170 (52.4) | 599 (56.0) | ||
| ≥30 | 65 (19.5) | 151 (14.1) | ||
| Missing | 4 (0.8) | 4 (0.4) | ||
| Duration of breast-feeding†(mos) | ||||
| Never | 73 (21.5) | 233 (21.8) | ||
| ≤6 | 69 (20.0) | 209 (19.5) | ||
| 7-12 | 104 (32.5) | 361 (33.7) | ||
| 13-24 | 55 (11.6) | 115 (10.8) | ||
| ≥25 | 77 (13.9) | 152 (14.2) | ||
| Duration of oral contraceptive use (y) | ||||
| Never used | 332 (89.0) | 978 (91.4) | ||
| ≤1 | 21 (5.8) | 35 (3.3) | ||
| ≥1 | 25 (5.3) | 56 (5.2) | ||
| Induced abortions | ||||
| 0 | 163 (40.7) | 437 (40.8) | ||
| 1 | 138 (37.1) | 427 (39.9) | ||
| ≥2 | 56 (16.8) | 167 (15.6) | ||
| Missing | 21 (5.4) | 39 (3.7) | ||
| Years since last induced abortion† | ||||
| None | 163 (40.7) | 437 (40.8) | ||
| 0-10 | 41 (14.6) | 129 (12.1) | ||
| 11-15 | 49 (16.7) | 185 (17.3) | ||
| 16-20 | 29 (7.6) | 120 (11.2) | ||
| >20 | 54 (10.1) | 145 (13.6) | ||
| Missing years | 42 (10.3) | 54 (5.1) | ||
| No. prior benign breast lumps | ||||
| 0 | 360 (94.5) | 1,038 (97.0) | ||
| 1 | 13 (3.9) | 22 (2.1) | ||
| ≥2 | 5 (1.6) | 10 (0.9) | ||
| Times breast self-examination/y‡ | ||||
| 0 | 198 (50.8) | 725 (67.8) | ||
| 1-6 | 80 (21.4) | 137 (12.8) | ||
| 7-12 | 85 (23.8) | 198 (18.5) | ||
| ≥13 | 10 (3.1) | 7 (0.7) | ||
| Missing | 5 (0.9) | 3 (0.2) | ||
| Menopause | ||||
| No | 187 (62.7) | 687 (64.2) | ||
| Yes | 191 (37.3) | 383 (35.8) | ||