Table 4.

Ever oral contraceptive use in relation to ER+PR+ and ERPR cancers according to categories of breast cancer risk factors

Risk factorER+PR+ERPR
OC use ever/never (no. cases)IRR* (95% CI)POC use ever/never (no. cases)IRR* (95% CI)P
Age (y)
    <50144/231.28 (0.82-2.00)0.07119/141.80 (1.03-3.15)0.87
    50+140/701.04 (0.77-1.41)114/321.59 (1.05-2.41)
Premenopausal130/191.36 (0.84-2.21)0.14106/151.49 (0.86-2.57)0.75
Postmenopausal112/270.95 (0.69-1.31)90/271.66 (1.05-2.62)
BMI at age 18 y (kg/m2)
    <20134/430.89 (0.61-1.29)0.55116/251.43 (0.91-2.25)0.42
    20+146/571.10 (0.79-1.54)116/211.85 (1.14-3.01)
Current BMI (kg/m2)
    <2569/190.94 (0.55-1.61)0.3562/111.53 (0.78-2.98)0.97
    25+214/831.13 (0.85-1.49)171/351.67 (1.14-2.44)
Age at menarche (y)
    <1277/281.05 (0.65-1.69)0.9077/181.41 (0.82-2.44)0.41
    12+206/741.10 (0.82-1.47)156/281.79 (1.18-2.73)
Age at first birth (y)
    <2062/290.99 (0.61-1.61)0.4457/141.56 (0.84-2.90)0.25
    20+150/471.02 (0.71-1.46)140/182.18 (1.31-3.62)
Parity
    072/241.54 (0.91-2.61)0.3334/141.00 (0.50-1.98)0.06
    1+212/780.99 (0.75-1.32)198/321.92 (1.30-2.83)
Female hormone use
    Never184/511.19 (0.85-1.66)0.29165/242.05 (1.32-3.19)0.12
    Ever98/491.04 (0.69-1.45)68/211.26 (0.74-2.14
Family history
    No229/851.39 (0.77-2.54)0.24194/392.15 (0.93-4.98)0.55
    Yes55/171.04 (0.79-1.37)39/71.59 (1.10-2.28)
Cigarette smoking
    Never170/541.23 (0.88-1.72)0.59141/261.53 (0.99-2.35)0.75
    Ever114/471.01 (0.69-1.47)92/201.83 (1.09-3.08)
Alcohol (drinks/wk)
    <1207/781.08 (0.81-1.43)0.82169/381.42 (0.98-2.05)0.49
    1+77/241.16 (0.69-1.94)64/82.81 (1.29-6.09)
Vigorous exercise
    No159/591.25 (0.90-1.74)0.24131/301.59 (1.05-2.42)0.72
    Yes122/410.89 (0.61-1.31)101/151.82 (1.04-3.21)
Education (y)
    <16143/491.39 (0.97-1.99)0.15139/291.77 (1.16-2.70)0.44
    16+141/530.87 (0.62-1.23)102/171.55 (1.07-2.31)
  • *Never use of oral contraceptives is the reference category; IRRs adjusted for age, age at menarche, BMI at age 18 y, family history of breast cancer, education, parity, age at first birth, menopausal status, age at menopause, menopausal hormone use, vigorous activity, and alcohol intake.

  • P value for interaction.