[Host defense mechanisms against tumor metastasis].

It is still difficult to control metastasis of cancers, despite advances in surgery and radio-therapy for primary lesions of cancers. The prevention of cancer metastasis is therefore a major target of cancer research. In order to analyse the mechanism of tumor metastasis, several in vivo and in vitro assay systems have been established and the effects of host and tumor factors on formation of tumor metastasis have been studied. It is known that specific immunity mediated by T cells and natural resistance mediated by macrophages and natural killer cells play a significant role in host defense mechanisms against tumor metastasis. I describe here my study of the effect of surgical operation of primary tumors on metastasis and of the suppression of tumor metastasis by activated natural host defense using an experimental model of spontaneous metastasis in spontaneously hypertensive rats (SHR).