Transplantability and metastatic potential of chemically induced rat brain tumours

From clinical observations it is known that brain tumours in principle do not metastasize. An explanation for this phenomenon is not available. The few described cases of distant metastases from primary brain tumours all occurred after surgery of the central nervous system. Furthermore, the brain does not contain a lymphatic system. The major question in this matter is whether the inability of CNS tumours to metastasize is based on a specific tumour bound property or on specific local factors. Since an experimental model for this situation was not available we induced brain tumours in rats. About 130 WAG/Rij and Sprague Dawley rats (males and females) were treated with the neurocarcinogen ethylnitroso-urea (ENU) within 24 hours after birth. Tumours appeared at the age of 6 to 29 months. All tumours were removed after killing the host and transplanted subcutaneously into syngeneic rats. Histologically the tumours were mostly oligodendrogliomas, schwannomas and several mixed glial tumours. Metastases from these primary tumours were not observed. The transplanted tumours showed distant metastases in 52% of the cases. Metastases occurred mainly in lungs, liver and lymph nodes. From these observations it is concluded that the absence of metastases from primary brain tumours is probably not related to a specific property of brain tumours. Further research is emphasized on specific local factors.