Abstract
A course of intravenous injections of Corynebacterium parvum starting 4 days before a single intramuscular injection of methylcholanthrene markedly delayed or prevented the development of fibro-sacromas in CBA mice. Similar treatment starting 4 weeks after injection of the carcinogen did not significantly alter the incidence of tumours. In the light of these findings, and previous work on the effect of C. parvum on macrophage activity and the growth of isogeneic tumour transplants, it is postulated that a transformational event occurs soon after injection of methylcholanthrene which results in the emergence of a clone of cells which are selectively liable to destruction by activated macrophages, but which, if not destroyed, multiply so rapidly that subsequent treatment fails to prevent, or even perceptibly to delay, the appearance of a tumour.
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