GSTM1 and neoplasm: Hypotheses that ESAs may promote tumour growth through erythropoietin receptor activation, stimulation of angiogenesis or through hypoxia improvement through Hb increases have also been proposed (Kelleher et al, 1998; Acs et al, 2001, 2002; Arcasoy et al, 2002; Yasuda et al, 2003; Janecka, 2004; Vaupel and Mayer, 2004).