Background: This study is the last part of a quadruple series investigating the relationship between breast disorders and the consumption of exogenous sex hormones. Due to the structural similarity of phytoestrogens to estrogen and the confusion associated with their possible estrogenic activity in the breast, this part aims at reviewing of the literature on the relationship between phytoestrogens and breast disorders. Methods: We carried out a thorough search of the existing literature using appropriate keywords with the aim of finding systematic reviews, reviews, cohort studies and clinical trials regarding the effects of phytoestrogens on the breast in the general population, breast cancer survivors, women at high risk of breast cancer and those with benign breast diseases. Results: Many studies have approached the relationship between phytoestrogens and the risk of breast cancer or recurrence of the disease. Also, a few studies have considered the effects of phytoestrogens on benign breast disorders, BRCA genes, and the risk of breast cancer in high risk women. However, the variety of studies and the retrospective nature of many of them make it impossible to draw definite conclusions. Conclusion: Existing data generally supports the safety of phytoestrogen consumption regarding the risk of breast cancer in the general population, in women with benign breast disorders, in those at risk of breast cancer, and even in survivors of the cancer. However, due to insufficient evidence, prescription of high doses of phytoestrogens is still not recommended.