Overexpression of Oncogene Products Can Cause Tumor Progression without Parenchymal Infiltration in the Rat Brain1

Tumor cell progression and parenchyma! infiltration play important roles in the pathogenesis of gliomas. Using retrovirally marked rat 9L gliosarcoma cells, which when injected in the CDF rat brain form noninfiltrating tumors which grow only surrounding existing blood ves sels, we were able to investigate elements of tumor growth and progression within the substance of the brain. Transfection of 9L by oncogenes associated with tumor progression and expressed in gliomas resulted in alterations in the in vivo phenotype of these cells, with the production of faster growing, well-vascularized, large solid tumors. However, diffuse ¡utili raÃion was not seen. Moreover, coinjection of 9L or its transfectants together with the infiltrative C6 cell line resulted in a mixed tumor of noninfiltrating 9L cells in an environment of infiltrating C6 cells, sug gesting that the ¡nfiltrativeability of C6 cells is controlled on the individual cell level.