Described are (a) parvovirus variants capable of propagating and spreading through human tumor cells which is obtainable by serially passaging a rodent parvovirus as starting strain in semi-permissive human tumor cells, and (b) parvovirus variants capable of propagating and spreading through human tumor cells characterized by particular amino acid deletions and/or substitutions, e.g. a deletion of several amino acids in the C-terminus of NS1/middle exon of NS2. A pharmaceutical composition containing such parvoviruses as well as their use for the treatment of cancer, preferably a glioblastoma, is also described.