Clinically relevant drugs known to be transported by MRP4 include nucleoside and nucleotide analogs (Chen et al., 2001) and, relevant to neuroblastoma, the camptothecins irinotecan (Norris et al., 2005) and topotecan (Tian et al., 2005) (Table 1). This evidence concerns the gene ABCC4 and neuroblastoma.