Hormone-dependent cancers, such as certain types of breast cancer, pose a significant clinical challenge due to the direct influence of sex hormones on tumor proliferation. Among these, tumors that are strongly estrogen receptor-positive (ER+) form a well-defined subtype that often responds favorably to hormone therapy, given the high expression of these receptors in neoplastic cells. In this context, diet plays a relevant role, particularly due to the presence of bioactive compounds like phytoestrogens. These compounds have a structure similar to estrogen and can interact with ERs, leading to debate about the potential benefits or risks of including phytoestrogen-rich foods in the diet of patients with ER+ breast cancer. Since scientific evidence is varied and in some cases contradictory, this paper will outline the current state of research on the topic.