Upon cessation of prodrug administration, all animals developed recurrent tumors, which could be classified into three different groups ( Figure 7B-E, table 2) . The animals showed either 1) local recurrences or 2) local and/or contralateral recurrences or 3) recurrences in other distant brain areas. There was no clear difference in the recurrence pattern between the two vector types, but LCMV-pseudotyped vector-treated animals had more contralateral recurrences, whereas VSV-G pseudotyped vector-treated animals had more local recurrences ( Figure 7B -E, table 2). Histopathological and confocal microscopic analysis of the lesions revealed GFP-positive cells in all recurrent tumors demonstrating that not all transduced glioma cells were killed by ganciclovir treatment (Figure 7F-M) . In VSV-G pseudotype-treated animals, the GFP-positive surviving cells were found in invasive areas ( Figure 7F ,G), the corpus callosum region ( Figure 7H ) and also in some regions of distant recurrences. One animal also showed a focus of transduced normal brain cells at the tumor border that survived GC treatment ( Figure 7I ). In the LCMV group, most GFP-positive cells were found in the ipsilateral hemisphere, in solid and invasive tumor areas ( Figure 7J ,K,L), with only a few cells seen in the contralateral hemisphere ( Figure 7M ).