Hormone-dependent cancers of the breast, prostate and colon have, in the past decade, become the leading causes of morbidity and mortality. Billions of dollars have been spent to study cancers like these, and tremendous advancements in the understanding and treatment of cancer have been made. Nevertheless, as effective cures for a variety of cancers continue to elude us, natural protection against cancer has been receiving a great deal of attention lately not only from cancer researchers and patients, but also from physicians. Phytoestrogens, plantderived secondary metabolites, are diphenolic substances with structural similarity to naturally-occurring human steroid hormones. Phytoestrogens are normally divided into three main classes: flavonoids, coumestans and lignans. Flavonoids are found in almost all plant families in the leaves, stems, roots, flowers and seeds of plants, and are among the most popular anti-cancer candidates. Flavonoidic derivatives have a wide variety of biological actions that includes antibacterial, antiviral, anti-inflammatory, anticancer, and antiallergic activities. Some of these benefits are explained by the potent antioxidant effects of flavonoids, which include metal chelation and free-radical scavenging activities. However particular phytoestrogens show a marked ability to induce programmed cell death in specific cancer cells, and delay or prevent the onset of discrete cancers altogether. Patent applications regarding flavonoids range from protocols for extraction and purification from natural resources and the establishment of various biological activities for these extracts to novel methods for the production and isolation of flavonoids with known biological activities. This review will bring the reader up to date on the current knowledge and research available in the field of flavonoids and hormone-dependent cancers, and some of the submitted patents that exploit flavonoids.