Lentinan is a high-molecular-weight beta-glucan polysaccharide extracted from the fruiting bodies of the shiitake mushroom Lentinula edodes. It consists of a linear backbone of beta-1,3-linked D-glucose residues with beta-1,6-linked side chains. Clinically used in Japan as an adjunct in cancer immunotherapy, it activates macrophages, natural killer cells, and T-lymphocytes via dectin-1 and TLR receptors, enhancing immune response against tumors. It exhibits immunomodulatory, antitumor, and antioxidant properties. As a large hydrophilic polymer, it is administered intravenously. Research from peer-reviewed studies confirms its role in improving survival rates in gastric and colorectal cancers when combined with chemotherapy. Its structure allows strong hydrogen bonding leading to high water solubility but poor solubility in organic solvents.