Spontaneous regional lymph node and pulmonary metastases after irradiation of B16 melanomas in foot-pads of C57BL/6 mice

Reports of the incidence of lymph node and pulmonary metastases after X-ray irradiation of primary tumors have been contradictory. Viable F10 variant of B16 melanomas were injected into right hind foot pads of syngeneic female C57BL/6 mice. At 2mm, tumors were irradiated: 30, 40, 55, 64.7, 72.5 Gy., Groups 1-5, respectively. Control mice underwent 19 min. of sham treatment; tumors grew to 5mm in 34 days post inoculation. Irradiated tumors were delayed in growth rate, the slowest correlating with the highest radiation dose. Irradiated mice had a significant increase (p=<0.047) in the number of pulmonary metastases. This investigation may indicate that lower dosage X-ray irradiation causes delay of tumor growth rate and increases metastases, while higher dosage may alter metastatic rates