Radiation therapy and Corynebacterium parvum in the treatment of murine tumors

The relative effectiveness of local irradiation alone or combined with Corynebacterium parvum (C parvum) treatment has been investigated employing four tumors: a mammary carcinoma (MCa) (nonimmunogenic), a fibrosarcoma (moderately strongly immunogenic), and two squamous cell carcinomas (SCC-2 being weakly and SCC-4 being very weakly or nonimmunogenic). C parvum treatment was started when the isotransplanted tumor growing in the mouse leg was 5 mm in diameter and the local irradiation was administered to 8-mm diameter tumor. Effect of the combined treatment was barely evident with the MCa but strongly present in FSa; up to 60% of mice were cured of FSa by C parvum alone and the response to low radiation dose, e.g., 200 rads, was highly increased. For SCC-2 the TCD50 was approximately 7000 rads and 3000 rads in control and test mice, respectively. Comparable values for SCC-4 were 7700 and approximately 5500 rads. Importantly, for SCC-4 there was a large and highly significant reduction in the proportion of mice that died of metastases to lung but were free of evident tumor at the primary site.