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Table 3 The effect of progesterone vs. synthetic progestins in combination with estrogen on breast cancer incidence

From: Progesterone vs. synthetic progestins and the risk of breast cancer: a systematic review and meta-analysis

Study Group 1 Incidence of breast cancer in group 1 Group 2 Incidence of breast cancer in group 2 Relative risk (RR) 95 % confidence interval (95 % CI)
Espie et al. 2007 [16] Estradiol + progesterone 4/999 Estradiol + synthetic progestina 12/1272 0.42 0.13–1.31
Fournier et al. 2008 [8] Estrogen + progesterone (almost exclusively estradiol compounds) 129/40,537 person-years Estrogen + synthetic progestin (almost exclusively estradiol compounds) 635/135,288 person-years 0.68 0.56–0.82
Estrogen + progesterone (almost exclusively estradiol compounds) 129/40,537 person-years Estrogen + synthetic progestinb (almost exclusively estradiol compounds) 606/128,253 person-years 0.67 0.76–0.81
  1. aThis study excluded users of medroxyprogesterone acetate and 19-nortestosterone derivatives
  2. bThis is a partial cohort that does not include users of medroxyprogesterone acetate from the analysis