Table 2.
Odds ratios (ORs) and 95% confidence intervals (95% CI) for the association between established reproductive risk factors and young-onset invasive and DCIS breast cancer, Two Sister Study (2008–2010)
| Characteristics | Control Sisters (n=1648) No. (%) |
Invasive Cases (n=1185) No. (%) |
DCIS Cases (n=221) No. (%) |
Adjusted OR All cases vs. controls (95% CI) |
Adjusted OR Invasive cases vs. controls (95% CI)) |
Adjusted OR DCIS cases vs. controls (95% CI) |
Homogeneity p-valuea |
|---|---|---|---|---|---|---|---|
| Age at Menarcheb | |||||||
| ≥14 | 433 (26) | 259 (22) | 55 (25) | 1.00 | 1.00 | 1.00 | |
| 12 or 13 | 942 (57) | 699 (59) | 127 (57) | 1.29 (1.06, 1.57) | 1.29 (1.04, 1.60) | 1.27 (0.76, 2.12) | p= 0.67 |
| <12 | 272 (17) | 227 (19) | 39 (18) | 1.45 (1.11, 1.89) | 1.51 (1.13, 2.01) | 1.05 (0.52, 2.11) | |
| Trend test | p =0.005 | p = 0.005 | p = 0.79 | ||||
| Menopausal status, index agec | |||||||
| Premenopausal | 1379 (84) | 1070 (90) | 186 (84) | 1.00 | 1.00 | 1.00 | |
| Postmenopausal, age at menopause <45 y | 116 (7) | 40 (3) | 15 (7) | 0.48 (0.33, 0.69) | 0.38 (0.25, 0.58) | 1.38 (0.58, 3.30) | p= 0.06 |
| Postmenopausal, age at menopause ≥45 y | 29 (2) | 16 (1) | 3 (1) | 0.56 (0.29, 1.10) | 0.68 (0.32, 1.43) | 0.42 (0.09, 2.10) | |
| Premenopausal hysterectomy, with retained ovarian tissue | 122 (7) | 59 (5) | 17 (8) | 0.68 (0.48, 0.94) | 0.64 (0.44, 0.93) | 0.96 (0.44, 2.10) | |
| Parity as of index aged | |||||||
| Nulliparous | 352 (21) | 252 (21) | 47 (21) | 1.00 | 1.00 | 1.00 | |
| 1 child | 256 (16) | 186 (16) | 38 (17) | 0.99 (0.76, 1.28) | 0.91 (0.69, 1.22) | 1.54 (0.73, 3.26) | p= 0.09 |
| 2 children | 613 (37) | 458 (39) | 90 (41) | 1.15 (0.92, 1.43) | 1.12 (0.88, 1.42) | 1.43 (0.77, 2.65) | |
| ≥3 children | 426 (26) | 289 (24) | 46 (21) | 1.08 (0.84, 1.38) | 1.15 (0.88, 1.50) | 0.80 (0.38, 1.66) | |
| Trend test | p = 0.61 | p = 0.17 | p = 0.17 | ||||
| Age at first pregnancy lasting ≥37 weeks (as of index age)e | |||||||
| <25 y | 465 (37) | 270 (30) | 54 (32) | 1.00 | 1.00 | 1.00 | |
| 25–29 y | 456 (36) | 341 (38) | 52 (31) | 1.28 (0.98, 1.66) | 1.35 (1.02, 1.79) | 0.83 (0.39, 1.77) | p= 0.32 |
| 30–34 y | 233 (19) | 214 (24) | 40 (24) | 1.65 (1.20, 2.28) | 1.58 (1.12, 2.23) | 1.89 (0.72, 4.95) | |
| ≥35 y | 100 (8) | 64 (7) | 22 (13) | 1.22 (0.80, 1.87) | 1.12 (0.70, 1.80) | 1.35 (0.42, 4.33) | |
| Trend test | p = 0.03 | p = 0.11 | p = 0.23 | ||||
| Breastfeeding History (among parous women; as of index age)f | |||||||
| Never | 265 (20) | 181 (19) | 28 (16) | 1.00 | 1.00 | 1.00 | |
| Ever | 1030 (80) | 752 (81) | 146 (84) | 1.08 (0.80, 1.48) | 1.02 (0.72, 1.44) | 1.24 (0.56, 2.73) | p= 0.27 |
| Use of oral contraceptives as of index ageg | |||||||
| Never User | 167 (10) | 112 (9) | 27 (12) | 1.00 | 1.00 | 1.00 | |
| Ever User | 1479 (90) | 1073 (91) | 194 (88) | 0.96 (0.74, 1.24) | 1.03 (0.77, 1.36) | 0.65 (0.34, 1.23) | p= 0.19 |
Abbreviations: Odds Ratio (OR), 95% Confidence Interval (95% CI), Ductal Carcinoma in situ (DCIS)
The following variables had missing data: Age at menarche (1 control), Menopausal status (2 controls), Parity (1 control), Breastfeeding (1 control), Use of oral contraceptives (2 controls). 13 cases were missing invasive status were removed, along with their 17 matched controls.
Likelihood ratio test for homogeneity between the invasive-specific OR and the DCIS-specific OR.
Adjusted for education (high school or less, some college but no degree, associate or technical degree, bachelor degree, master or doctoral degree), relative weight at age 10 (lighter, same, heavier), childhood physical activity (0, <2 hrs, 2–<4, ≥4 hrs/wk)
Adjusted for education, age at menarche (<12, 12 or 13, >13), birth order (1, 2, or 3+) BMI in 30s (<18.5, 18.5–24.9, 25.0–29.9,≥30.0 kg/m), parity (0, 1–2, 3+ births), smoking (ever/never)
Adjusted for education, age at menarche, birth order, oral contraceptive use (never/ever), age at first live birth (continuous, data for nulliparous women imputed with mean value)
Among women with at least one term pregnancy; Adjusted for education, age at menarche, birth order, oral contraceptive use (never/ever)
Adjusted for education, age at first live birth (continuous), alcohol use (ever/never), smoking, birth order
Adjusted for education, age at menarche, birth order