Table 2. Clinical, exogenous hormonal, and menstrual and reproductive factors and their association with breast cancer.
| Variables | Cases/Controls | OR(95%CI)3 | OR(95%CI)4 |
|---|---|---|---|
| Ever had breast surgery | |||
| No | 972/1,807 | ||
| Yes | 249/214 | 2.42(1.96–3.00)*** | 2.27(1.82–2.83)*** |
| First degree family history of breast cancer | |||
| No | 3,170/3,478 | ||
| Yes | 513/502 | 1.10(0.96–1.27) | 1.19(1.02–1.38)* |
| Ever use oral contraceptives | |||
| Never | 2,452/2,806 | ||
| Ever | 935/1,145 | 1.02(0.91–1.14) | 0.99(0.88–1.11) |
| Ever use hormonal replacement therapy1 | |||
| Never | 419/1,452 | ||
| Ever | 51/259 | 0.52(0.44–0.61)*** | 0.48(0.4–0.58)*** |
| Age of menarche | |||
| ≤12 | 1,178/1,611 | ||
| >12 | 1,714/2,329 | 1.04(0.94–1.15) | 1.04(0.94–1.16) |
| Menopausal status | |||
| Pre/Peri-menopausal | 1,149/1,550 | ||
| Post-menopausal | 1771/2,408 | 1.53(1.33–1.76)*** | 1.52(1.32–1.75)*** |
| Age of menopause (years)1 | |||
| ≤50 | 217/862 | ||
| >50 | 246/822 | 0.86(0.71–1.03) | 0.89(0.73–1.08) |
| Ever had full term pregnancy | |||
| Nulliparous | 473/552 | ||
| Parous | 2,778/3,366 | 1.05(0.91–1.20) | 1.13(0.97–1.31) |
| Parity2 | |||
| 1 | 319/337 | ||
| 2 | 828/974 | 0.97(0.81–1.18) | 1.09(0.82–1.46) |
| 3 | 800/1,020 | 0.97(0.8–1.17) | 0.98(0.73–1.32) |
| 4 | 460/586 | 1.12(0.91–1.38) | 0.99(0.72–1.38) |
| ≥5 | 370/449 | 1.49(1.19–1.86)*** | 1.20(0.85–1.69) |
| Age of first full term pregnancy2 | |||
| <25 | 925/940 | ||
| 25–29 | 1,039/1,506 | 1.09(0.87–1.37) | 1.0(0.79–1.28) |
| ≥30 | 744/845 | 1.38(1.08–1.77)* | 1.29(0.99–1.67) |
| Ever breastfed2 | |||
| Never | 532/684 | ||
| Ever | 942/2,514 | 0.56(0.48–0.65)*** | 0.65(0.55–0.78)*** |
| Breastfeeding duration in months2 | |||
| None | 532/684 | ||
| ≤12 | 766/1,678 | 0.60(0.51–0.7)*** | 0.73(0.61–0.88)*** |
| >12 | 173/836 | 0.40(0.32–0.5)*** | 0.30(0.22–0.4)*** |
*p<0.05;
***p<0.001
1Natural menopause;
2Parous women only
3 Adjusted for age, ethnicity, and hospital, except history of breast surgery, which is adjusted for age, ethnicity, and education and only participants from private hospital are included
4Adjusted for age, ethnicity, hospital and breast cancer risk factors (age of menarche, menopausal status, ever had full term pregnancy, first degree family history of breast cancer, parity, age of first full term pregnancy, ever breastfed, breastfeeding duration when appropriate), except history of breast surgery, which is adjusted for age, ethnicity, education and relevant breast cancer risk factors, and only participants from private hospital are included