ABCG2 and neoplasm: Immunohistochemical analysis of ABCG2 expression in tumours, formed following the injection of 1×103 ABCG2hi SP cells in comparison to the residual cell pellets (which were not associated with any active growth) harvested from mice injected with ABCG2low NSP sorted RT112 cells, showed increased expression in ABCG2hiSP compared with ABCG2lowNSP derived tumours (Figure 4B).