II. Tumor growth at sites of inflammation induced by mitogens in mice

Experiments were carried out to determine whether the growth of tumors could be influenced by local inflammatory reactions induced by mitogens; Gram-negative bacterial lipopolysaccharide (LPS), concanavalin A (Con A) and phytohemagglutinin (PHA). Mice received injections, beneath the footpad or subcutaneously in the flank, of cells of syngeneic chemically induced fibrosarcomas with or without varying doses of mitogen. In the footpad (a) LPS caused a dose-dependent increase in the size; (b) Con A caused a decrease in the size of one of the three tumors, the decrease being inversely related to the dose of Con A; (c) PHA caused a dose-dependent decrease in the size of all three tumors: (d) PHA caused much smaller macroscopic inflammatory reactions than LPS or Con A. Subcutaneously injected tumor growth was inhibited by all three agents. Subcutaneous tumors contained a higher proportion of host inflammatory cells when mitogens had been mixed with the tumor inoculum. It is concluded that mitogens that can induce inflammatory reactions in mice can also bring about some suppression of tumor growth but that the depression is site-dependent and not clearly related to the apparent intensity of inflammation.