Effect of second tumors and of prostaglandin-leukotriene inhibitors on radiation therapy of transplanted rodent tumors.

The prostaglandin and leukotriene inhibitor sodium meclofenamate (SM) failed to influence radiation therapy induced regression of 6C3HED Gardner lymphosarcoma in C3H mice. Recurrence after radiation therapy, however, was reduced by treatment with SM. During these experiments, we observed that if a tumor was "cured" by radiation therapy, it required inoculation of a larger number of cells to establish a second tumor. Presumably, a certain degree of immunity has developed. On the other hand, if a second tumor was already established, less tumor cells were needed to establish a third tumor. This may be related to immuno-suppressor products of the second tumor. This effect could be partly inhibited by SM, suggesting that prostaglandins and leukotrienes may be involved in this phenomenon.