In order to evaluate clinical efficacy of Lentinan (LNT), a purified polysaccharide extracted from Lentinus edodes, randomized controlled studies with envelope method have been conducted on the patients with advanced or recurrent, stomach, colo-rectal and breast cancer. Administration condition of LNT for gastrointestinal cancer was designed as the following: LNT was administered intravenously at doses of 1 mg/person/day twice a week or 2 mg/person/day once a week in combination with mitomycine C + 5-FU (MF) or tegafur (FT). Control therapy was the administration of MF or FT alone. Survival curve drawn by Kaplan-Meier's method showed that life span prolongation effect of LNT was observed with statistical significance (P less than 0.05 or P less than 0.01) by use of generalized Wilcoxon's test. Moreover, improvement of host immune responses was observed in LNT treated group, and hematological survey showed that incidence rate of abnormal value was significantly low in LNT treated group. Thus, LNT should be effective for the patients with advanced or recurrent stomach or colo-rectal cancer in combination with chemotherapeutic agents such as MF or FT. Regarding advanced or recurrent breast cancer, study is underway. LNT has been administered as an agent for supportive therapy to the patients with complete response, partial response or stable diseases which were induced by prior surgery of oophorectomy. Again, life span prolongation effect of LNT has been observed with statistical significance (P less than 0.05). This result suggests that LNT would also be effective for the patients with advanced or recurrent breast cancer as an agent for supportive therapy.