The antimetastatic effect of IV-inoculated BCG on adenocarcinomas in the prostate-seminal vesicle complex of L-W rats.

Adenocarcinomas were induced in the prostate-seminal vesicle complex of Lobund-Wister (L-W) rats by a single IV inoculation of N-methyl-N-nitrosourea. This was followed by three slow-release S.C. implants of testosterone propionate, each at intervals of 2 months. Small (0.5 cm diameter) palpable tumors developed which enlarged during the following month to 3-4 cm diameter. At the latter stage, tumor cells spread via lymphatics to the lungs and/or by direct extension into the peritoneal cavity. Rats with small palpable tumors were inoculated IV with viable Bacillus Calmette-Guerin (BCG). One month later, the rats were killed and examined. Untreated rats with large tumors served as controls. Comparison of the two groups revealed that body weights and tumor sizes were similar and most of them had developed metastatic tumors in the peritoneal cavity. However, lung metastases were rare in the BCG-inoculated rats compared to controls. Spleen and liver weights were significantly heavier in the BCG-treated rats. It is speculated that an intra-vascular mechanism(s), engendered by BCG, immobilized the circulating tumor cells, but not those tumor cells that spread by direct extension from the primary tumor into the peritoneal cavity.