Stimulation of tumor growth in mice by high doses of BCG

The growth of Krebs-2 carcinoma in BCG-prevaccinated virgin female C57BL/6, CC57BR/M, and C3Hf mice was studied in relation to the number of living mycobacteria in the organism. When the number of mycobacteria was high, tumor growth was stimulated. After the bacteria were eliminated, tumor growth was inhibited. The effect of BCG was based, on the one hand, on the diversion of effector cells, presumably macrophages, responsible for tumor defense and, on the other hand, on the activation of the pool of these cells. The conclusions were reached that high doses of BCG may be dangerous in human cancer immunotherapy and that patients predisposed to neoplastic disease should be revaccinated with BCG.