Effect of a single injection of cyclophosphamide on immunization therapy of metastases remaining after excision of dermal primary tumors in guinea pigs.

Guniea pigs with established (7 or 14 days old) syngeneic dermal tumors and metastases in the draining lymph nodes were unsuccessfully treated by excision of the dermal tumors and specific immunization. The vaccines consisted of killed BCG in oil in an emulsified form admixed with mitomycin C treated or irradiated tumor cells. The therapeutic failure to eradicate the metastases was overcome by an additional treatment with a single injection of cyclophosphamide prior to excision of the primary tumor and immunization. It is assumed that cyclophosphamide destroys suppressor elements in the tumor-bearing guinea pigs and, in this way, augments the therapeutic effects of specific immunization.