Table 3.

Type of progestin formulation among current oral contraceptive users and RR of breast cancer compared with never oral contraceptive users (Nurses' Health Study II)

Person-yearsCasesAge-adjusted RR (95% CI)Multivariate* RR (95% CI)P
Never OC use176,5811621.00 (reference)1.00 (reference)
Current use
    Progestin type
        Norethindrone27,561120.82 (0.46-1.48)0.81 (0.45-1.45)0.47
        Triphasic17,24840.50 (0.19-1.37)0.50 (0.18-1.35)0.17
    Norethindrone
        Norethindrone acetate10,744151.39 (0.82-2.37)1.34 (0.79-2.28)0.28
        Ethynodiol diacetate5,60741.35 (0.50-3.65)1.22 (0.45-3.32)0.70
        Triphasic16,688263.05 (2.00-4.64)3.05 (2.00-4.66)<0.0001
    Levonorgestrel
        Levonorgestrel6,66240.87 (0.32-2.35)0.86 (0.32-2.34)0.77
        Norgestrel12,025121.85 (1.02-3.33)1.89 (1.05-3.41)0.04
Other21,584211.31 (0.83-2.07)1.27 (0.80-2.01)0.32
  • *Multivariate model controls for age (in months), follow-up cycle, body mass index (in kg/m2), family history of breast cancer (mother, sister, maternal grandmother, or paternal grandmother), menopausal status, history of benign breast disease, age at menarche, history of irregular menstrual periods, current pregnancy, parity, age at first birth, duration of breast-feeding, cigarette smoking, animal fat intake, alcohol consumption, and history of ovulatory infertility.

  • “Other” includes: norethynodrel, desogestrel, monophasic norgestimate, triphasic norgestimate, medroxyprogesterone, chlormadinone, dimethisterone, and unknown brands for current users.