Antitumor Effect of PSK: Role of Regional Lymph Nodes and Enhancement of Concomitant and Sinecomitant Immunity in the Mouse

PSK, a Coriolus preparation, inhibited the growth of not only the right but also the left, non‐treated tumor in a double grafted tumor system. In order to examine the role of lymph nodes and the spleen in the antitumor activity of PSK, regional (axillary and inguinal) lymph nodes and spleen were resected. Since in resected mice the antitumor activity of PSK against the right and left tumors was weakened, the regional lymph nodes and the spleen probably have a very important role in the antimetastatic effect of intratumoral administration of PSK. TIL (tumor‐infiltrating lymphocytes) obtained from left and right side tumors treated with PSK were examined by Winn assay for their antitumor activity against Meth‐A sarcoma in BALB/c mice. TIL from both sides clearly inhibited the growth of admixed Meth‐A cells, but control TIL did not. A primary growth of Meth‐A sarcoma inoculated into the right flank resulted in the generation of concomitant immunity to the growth of a second graft of the same tumor cells in the left flank. A significant inhibitory effect on the proliferation of the tumor cells inoculated secondarily was shown in mice bearing a primary right tumor that had previously been inoculated with PSK 3 times. After surgical excision of the primary tumor on day 6, daily oral administration of PSK significantly inhibited the growth of the secondary tumor inoculated on day 21, that is, PSK treatment also enhanced sinecomitant immunity. These observations suggest that presurgical intratumoral injection and postoperative oral administration of PSK are highly effective in eradicating metastatic tumors.