INFLUENCE OF IRRADIATION OF A PRIMARY TUMOR ON THE LABELING INDEX AND ESTROGEN-RECEPTOR INDEX IN A DISTANT TUMOR FOCUS

The present investigation reaffirms our observation that removal of a C3H mouse mammary adenocarcinoma results in a perturbation of tumor cells in a metastatic focus. An increase occurs in the proportion of cells undergoing DNA synthesis (labeling index, LI), and a decrease occurs in the proportion demonstrating estrogen receptor (ER index; ERI). The changes are transient but of sufficient duration and magnitude to produce an increase in the size of a distant tumor. This study was conducted to determine whether cytoreduction of a primary tumor by irradiation would produce a similar change in metastatic tumor cells and whether preoperative radiation would obtain the effect of primary tumor removal. The administration of a maximum tolerated dose of radiation (50 Gy) to a primary tumor produced a significant (p < 0.001) increase in LI and decrease in ERI of a lesser magnitude than that observed following surgical removal of the primary tumor, but still sufficient to enhance the growth of a metastatic focus. Whereas, there was almost a 50% increase in LI in a metastasis 1 and 3 days following removal of a primary tumor the increase was only 13% three days after radiation. There was a 20% decrease in ERI 3 days following radiation and a 37% decrease at that time following tumor removal. Preoperative irradiation of a primary tumor 1, 3, or 5 days prior to tumor removal, obtunds the increase in LI and decrease in ERI following operation. Radiation the day before surgery was most effective because the changes in a distant focus occurring as a result of the radiation and of the surgery were prevented. The clinical relevance of these observations deserves further consideration.