The following are protective factors for breast cancer:
Less exposure of breast tissue to estrogen made by the body
Taking estrogen-only hormone therapy after hysterectomy, selective estrogen receptor modulators, or aromatase inhibitors and inactivators
Estrogen-only hormone therapy after hysterectomy
Selective estrogen receptor modulators: In the MORE trial, the relative risk reduction for raloxifene was 76%.[2] The P-1 preventative study demonstrated that tamoxifen can prevent breast cancer in high-risk individuals. The relative risk reduction was up to 50% of new breast cancers, though the cancers prevented were more likely estrogen-receptor positive (this is analogous to the effect of finasteride on the prevention of prostate cancer, in which only low-grade prostate cancers were prevented).[3][4]
Aromatase inhibitors and inactivators
Risk-reducing mastectomy: Bilateral prophylactic mastectomies have been shown to prevent breast cancer in high-risk individuals, such as patients with BRCA1 or BRCA2 gene mutations. [5]
Ovarian ablation: Prophylactic oophorectomy (removal of ovaries), in high-risk individuals, when child-bearing is complete, reduces the risk of developing breast cancer by 60%, as well as reducing the risk of developing ovarian cancer by 96%.[5]
↑Cummings SR, Eckert S, Krueger KA; et al. (1999). "The effect of raloxifene on risk of breast cancer in postmenopausal women: results from the MORE randomized trial. Multiple Outcomes of Raloxifene Evaluation". JAMA. 281 (23): 2189–97. PMID10376571.CS1 maint: Explicit use of et al. (link) CS1 maint: Multiple names: authors list (link)
↑Fisher B, Costantino JP, Wickerham DL; et al. (2005). "Tamoxifen for the prevention of breast cancer: current status of the National Surgical Adjuvant Breast and Bowel Project P-1 study". J. Natl. Cancer Inst. 97 (22): 1652–62. doi:10.1093/jnci/dji372. PMID16288118.CS1 maint: Explicit use of et al. (link) CS1 maint: Multiple names: authors list (link)
↑Fisher B, Costantino JP, Wickerham DL; et al. (1998). "Tamoxifen for prevention of breast cancer: report of the National Surgical Adjuvant Breast and Bowel Project P-1 Study". J. Natl. Cancer Inst. 90 (18): 1371–88. PMID9747868.CS1 maint: Explicit use of et al. (link) CS1 maint: Multiple names: authors list (link)