β-Glucans and their applications in cancer therapy: focus on human studies

β-glucans belong to a group of polysaccharides located in the cell wall of bacteria, fungi including mushrooms, as well as cereals such as barley and oats. All β-glucans are glucose polymers linked together by a (β 1-3) linear β-glycosidic chain core and they differ by their length and branching structures. They are considered biological response modifiers with immunomodulatory and health beneficial effects including anticancer properties. Few studies using purified β- glucans were performed, but their anticancer potential was demonstrated mainly through studies using extracts from mushrooms, yeast or other sources which contain β-glucan as a key component. Their anticancer effects were demonstrated mainly in in vitro and in vivo experimental systems but fewer studies from human populations are available. β-glucans have been used as adjuvant therapy in clinical trials, mainly in the Far East, with a positive effect on patients'survival and quality of life. The mechanism of action is suggested to be through its stimulation of the immune system. This review focuses on human studies; clinical trials and epidemiological data assessing the efficacy and safety of mushroom-derived β- glucans in cancer treatment and prevention. The potential direct effects of β-glucans on cancer cells are also described.