- Testing of patient's archived (paraffin embedded, unstained slides) or freshly biopsied tumor nodules must be positive for WT1 protein expression. WT1 expression: Immunohistochemical analysis will be performed using the technique described by Dupont et al [58]. WT1 expression will be graded according to an adaptation of the German Immunoreactive Score (IRS). Only tumors with moderate to strong IRS scores (4-12) will be considered WT1 positive.