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

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

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 progestin^a	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
Fournier et al. 2008 [8]	Estrogen + progesterone (almost exclusively estradiol compounds)	129/40,537 person-years	Estrogen + synthetic progestin^b (almost exclusively estradiol compounds)	606/128,253 person-years	0.67	0.76–0.81

^aThis study excluded users of medroxyprogesterone acetate and 19-nortestosterone derivatives
^bThis is a partial cohort that does not include users of medroxyprogesterone acetate from the analysis

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