Thus, together with our demonstration of PBOX-15-induced apoptosis in lenalidomide-refractory patient sample no. 4, and our previous work identifying the ability of PBOX-15 to induce apoptosis in p-glycoprotein-positive and breast cancer resistance protein-positive cancer cells (Nathwani et al, 2009), both of which have been shown to be associated with chemotherapy-induced treatment drug resistance in myeloma (Grogan et al, 1993; Turner et al, 2006), we suggest a potential role for PBOX-15 in the treatment of chemoresistant myeloma. This evidence concerns the gene ABCG2 and cancer.