Pathological examination of intracranial tumor mass in NC nude mice. A, SU-1 cells produced relatively well-delimited tumor masses (HE × 20). B, local amplification of A, showing nodular tumor formation (HE × 100). C, SU-2 cells behaved more aggressively (HE × 20). D, SU-2 cells infiltrated remoter regions and invaded the whole brain evenly and densely (HE × 200).