[Experimental studies on the effect of local irradiation on pulmonary metastasis]

The enhancement of pulmonary metastasis by local irradiation of primary tumor was investigated using Lewis lung cancer (3LL) and C57BL mice. One million 3LL cells were implanted at foot pads of mice and 7 days after the tumor-bearing legs were irradiated locally (60 Gy). Seven days after irradiation, mice were sacrificed and pulmonary metastatic nodules were counted. So it was confirmed that the pulmonary metastasis of tumor-irradiation group was enhanced significantly compared with control group and sham radiation group. The tumor-bearing legs were amputated just after, 1 day and 3 days after irradiation and pulmonary metastatic nodules were counted 7 days after irradiation. The pulmonary metastasis of mice whose legs were amputated 3 days after irradiation were enhanced significantly compared with control, though in other 2 groups pulmonary metastasis was not enhanced. So it was speculated that the enhancement of pulmonary metastasis needs remaining of irradiated tumor in bodies of mice for a certain period. It was confirmed by Winn assay that spleen cells of mice bearing irradiated tumors had an enhancing effect on tumor cells. And by Winn assay with pretreatment of cyclophosphamide, it was speculated that the enhancing effect was originated from suppressor T lymphocytes. So it was speculated that an enhancement of pulmonary metastasis by tumor irradiation was resulted from induction of suppressor T lymphocytes.