Further work is also needed to investigate the interplay of cytokine signalling pathways with transcription factors known to be relevant to drug-metabolising and transporting genes such as hepatocyte nuclear factor-4α, signal transducer and activators of transcription 3, CCAAT enhancer binding proteins and the pregnane X receptor, in order to further understand the mechanism by which IL-6 regulates drug clearance in the presence of tumours (Roy-Chowdhury et al, 2003; Tirona et al, 2003). This evidence concerns the gene STAT3 and neoplasm.