The therapeutic effects of an immunopotentiator,PS-K,on 3-methylcholanthrene-induced autochthonous tumors in C57BL/6 mice in combination with the surgical removal of primary sites

Summary We investigated the therapeutic effects of an immunopotentiator PS-K on recurrent or metastatic tumors observed after the surgical removal of MCA-induced primary tumors in autochthonous C57BL/6 mice and on the survival time of treated mice. The MST of mice treated with PS-K at various times (59.8 63.4 days) was prolonged as compared with that of mice treated by surgery alone (48.6 days). Local recurrence of tumors was found in 36 of 66 mice (54.6%) treated by surgery alone, whereas it was inhibited significantly (P<0.05) when treatment with PS-K was started 1 day after the surgery and occurred in 22 of 64 mice (34.4%) when PS-K was given for 5 days in 1 week, or in 22 of 66 mice (33.3%) when PS-K was administered twice a week for 7 weeks. The MSTs of mice with local recurrence were also found to be prolonged as compared with those of mice treated by surgery alone (54.8 67.5 days vs 49.8 days). The MSTs of mice without tumor recurrence were also prolonged significantly (P<0.05 0.001) by combinations of PS-K at various times, although most of the mice died of metastatic tumors even in the groups of mice where a combined treatment with PS-K had been administered. The above findings suggest that the administration of PS-K inhibits the growth of recurrent or metastatic tumor cells in autochthonous mice after the surgical removal of the primary tumors.This work was supported in part by Grants in Aid for Cancer Research from the Japanese Ministries of Education, Science and Culture and of Health and Welfare Abbreviations used: MCA; 3-methylcholanthrene, CY; cyclophosphamide, MST; mean survival time