Table 2.
BC risk associated with number of childbirths and breastfeeding duration according to HR status among BC cases and population-based matched controls in the Korea Breast Cancer Study, 2004 to 2012
| Total women |
Premenopausal women |
Postmenopausal women |
||||
|---|---|---|---|---|---|---|
| HR+ | HR- | HR+ | HR- | HR+ | HR- | |
| No. of childbirths | ||||||
| 0 | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) |
| 1 | 0.78 (0.61, 0.99) | 1.25 (0.87, 1.79) | 0.94 (0.69, 1.30)2 | 1.64 (0.96, 2.78)2 | 0.57 (0.39, 0.85)2 | 0.88 (0.53, 1.47)2 |
| 2 | 0.52 (0.44, 0.60)1 | 1.04 (0.83, 1.30)1 | 0.62 (0.50, 0.78)2,3 | 1.31 (0.92, 1.86)2 | 0.48 (0.37, 0.61)2,3 | 0.78 (0.57, 1.07)2 |
| 3+ | 0.39 (0.34, 0.46)1 | 1.05 (0.86, 1.18)1 | 0.55 (0.48, 0.61)2 | 1.39 (0.99, 1.83)2 | 0.22 (0.18, 0.25)2 | 0.73 (0.57, 0.99)2 |
| Breastfeeding duration (mo) | ||||||
| 0 | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) | 1.00 (reference) |
| 1-12 | 0.74 (0.69, 0.80) | 0.77 (0.68, 0.87) | 0.67 (0.61, 0.73)2,3 | 0.65 (0.55, 0.77)2 | 1.03 (0.89, 1.20)2,3 | 0.94 (0.78, 1.13)2 |
| 13-24 | 0.52 (0.48, 0.57) | 0.52 (0.46, 0.60) | 0.53 (0.48, 0.59) | 0.48 (0.39, 0.58) | 0.64 (0.55, 0.74) | 0.55 (0.46, 0.67) |
| 25+ | 0.40 (0.37, 0.44) | 0.40 (0.34, 0.47) | 0.45 (0.38, 0.52) | 0.49 (0.37, 0.66) | 0.48 (0.41, 0.57) | 0.40 (0.32, 0.49) |
Values are presented as OR (95% CI).
The OR (95% CI) in all women was estimated in conditional logistic regression stratified by age and enrollment year and adjusted for family history of BC, age at menarche, age at first full-term pregnancy, duration of oral contraceptive use, BMI, and breastfeeding duration in the analyses of parity and number of childbirths; or adjusted for family history of BC, age at menarche, age at first full-term pregnancy, duration of oral contraceptive use, BMI, and number of childbirths in the analyses of breastfeeding and its duration.
HR, hormone receptor; BC, breast cancer; OR, odds ratio; CI, confidence interval; BMI, body mass index.
p-value for the heterogeneity of two ORs (95% CIs) from HR+ subgroup and HR- subgroup in total women: <0.001 for [childbirths=2]; <0.001 for [childbirths=3+].
p-value for the heterogeneity of four ORs (95% CIs) from 4 subgroups classified by HR and menopausal status: 0.017 for [childbirths=1]; <0.001 for [childbirths=2]; <0.001 for [childbirths=3+]; <0.001 for [breastfeeding=1-12 months].
p-value for the heterogeneity of two ORs (95% CIs) from 2 subgroups classified by menopausal status in HR+ groups = 0.134 for [childbirths=2]; <0.001 for [breastfeeding=1-12 months].