Inhibitory effect of prolonged Corynebacterium parvum and cyclophosphamide administration on the growth of established tumors.

The present study was carried out to investigate the effects of prolonged administration of C. parvum alone and in combination with cyclophosphamide for the treatment of established, measurable C3H tumors. The continued weekly administration of C. parvum by itself provided a limited but significant inhibitory effect on tumor growth and significantly prolonged survival. Intraperitoneal and intravenous administration was found to be more effective than the subcutaneous route. When C. parvum was administered asynchronously in combination with cyclophosphamide at weekly intervals a tumor growth inhibitory effect was achieved which was greater than that resulting from either agent along. Such an effect was consistently obtained and was seemingly independent of the sequence of drug administration. When cyclophosphamide preceded the initial C. parvum administration, arrest in the rate of tumor growth occurred, resulting in infinite tumor doubling time for the duration of observation (greater than 90 days). The combination of C. parvum and cyclophosphamide produced a more effective inhibition of tumor growth than did BCG and cyclophosphamide similarly employed. The importance of these findings relative to clinical application is considered. While the significance and genesis of the marked desmoplastic reaction characterizing tumors from animals treated with C. parvum and cyclophosphamide is at present speculative, consideration is given to the possibility that this could signify a host response against tumor growth.