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Abstract: Cancer therapy now undertaken might be divided into three methods; operation, radiation, and chemotherapy. Almost all drugs used for cancer chemotherapy show a direct cytocidal effect against cancerous cells, and so they injure normal cells at the same time, especially bone marrow and lymphoid cells unselectively. Drugs, whose acts are based on their cytocidal effects, must be adopted for a selective cytotoxicity against cancer to avoid fatal side effects. In the above situation, immunotherapy has widely been investigated for cancer chemotherapy. There are several pieces of evidence suggesting the existence of intrinsic resistance against cancer. An example is the spontaneous curing of cancers. An increase in the resistibility may be one of the most important factors in the development of new methods of cancer chemotherapy. Based on such a concept, we have re-examined the anticancer activity of several folk remedies and found that hot water extracts of several basidiomycetes of Polyporaceae family, such as Ganoderma applanatum (PERS.) PAT., Phellinus linteus (BERK et CURT.) AOSHIMA and Coriolus versicolor (FR.) QUEL and edible mushrooms such as Lentinus edodes (BERK.) SING., and Flammulina velutipes (CURT ex FR.) SING, inhibited the growth of sarcoma-180 transplanted subcutaneously in mice. Important studies have been made on the effects of various immunopotentiators against cancers. These include lipopolysaccharides of Serratia marcescens. Zymosan, BCG, and Corynebacterium parvum. These immunopotentiators are all interesting and useful substances, but their physical and chemical properties are somewhat ambiguous. The present report is concerned with the preparation of the new antitumor polysaccharides such as Lentinan, Pachymaran, and Carboxymethylpachymaran. The relationships between structure and antitumor activity of these polysaccharides will be discussed from the view points of their planar and higher structures. Finally, the hypothesis on the restoration of lowered immune response of tumor bearing host by the antitumor polysaccharides will be proposed upon the basis of biochemical studies on interaction of antitumor polysaccharides with serum protein, and some immunological studies carried out by us and other groups will also be discussed.
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