Although the reversal of anaemia in the cancer patient is a desirable objective, the use of Epo in this context has recently been questioned by the discovery of the EpoR on tumour cells (Westenfelder and Baranowski, 2000; Acs et al, 2001; Arcasoy et al, 2003) and on endothelial cells (Anagnostou et al, 1994), leading to fears that some tumours use Epo as a growth factor, or that it may promote angiogenesis (Lappin et al, 2002). The gene discussed is EPO; the disease is anemia (phenotype).