Table 2.

Years since last use and duration of use of oral contraceptives in relation to breast cancer incidence by receptor status

UsePerson-yearsER+/PR+ER+/PRER/PR
No. casesIRR (95% CI)No. casesIRR (95% CI)No. casesIRR (95% CI)
Never used128,7681021.00 (reference)*291.00 (reference)461.00 (reference)
Ever used445,8242841.11 (0.86-1.42)800.97 (0.61-1.54)2331.65 (1.19-2.30)
Years since last use
    <5139,891441.29 (0.85-1.96)121.42 (0.63-3.21)431.97 (1.21-3.20)
    5-949,283241.53 (0.94-2.50)40.99 (0.32-3.04)121.23 (0.63-2.41)
    10+256,6492161.07 (0.83-1.37)640.94 (0.59-1.50)1781.64 (1.17-2.29)
Duration (y)
    <5250,6481501.03 (0.79-1.35)430.91 (0.55-1.49)1391.67 (1.18-2.36)
    5-9110,142641.09 (0.78-1.52)251.31 (0.74-2.33)441.37 (0.89-2.11)
    10-1463,348521.45 (1.02-2.07)90.82 (0.37-1.78)351.83 (1.11-2.90)
    15+21,686181.24 (0.74-2.09)30.75 (0.22-2.54)152.25 (1.23-4.11)
  • *Never use of oral contraceptives is the reference category; IRRs are adjusted for age, questionnaire cycle, age at menarche, BMI at age 18 y, family history of breast cancer, years of education, parity, age at first birth, age at menopause, menopausal hormone use, vigorous activity, and alcohol intake.