The tendency of using herbs extracts or natural compounds extracted from herbs for preventing or treating different illnesses, including cancer, continues to be an alternative to drug use. Many studies of plant compounds aimed at finding substances with selective cytotoxicity on abnormal cells. Phenolic compounds, as important secondary metabolites from plants, are one of them. In this review, the recent literature data from the past five years about anticancer/antitumor effect of flavonoids and tannins extracted from medicinal plants are surveyed. The cytostatic/antitumor effects of the individual compounds extracted from plants and/or of the plants' polyphenolic extracts are considered, in order to point out the most significant constituents or plants with anticancer potential. The most important results concerning these compounds and their derivatives in cancer prevention and treatment, the importance of their chemical structure, their mechanism of action in vitro and in vivo, and some bioavailability aspects are discussed.

Since early times, various plants have been used as remedies for treating different kinds of diseases and lesions with satisfying results. The phenolic compounds are secondary metabolites from medicinal plants which include a wide category of compounds such as phenolic acids, flavonoids, tannins, stilbenes, curcuminoids, xanthones, coumarins, lignans, etc. Between these, lignans are considered important in cancer prevention and treatment, besides other beneficial health effects, e.g. antioxidant, anticarcinogenic, antimutagenic, and anti-estrogenic effects. This review summarizes the most recent literature and the most important results concerning plant lignans and their derivatives in cancer prevention and treatment, both in vitro and in vivo assessments. The mechanistic aspects will be also highlighted.