Translocation of EpoR to the cell surface is an inefficient process (less than 1% of total cellular EpoR molecules are produced on the cell surface); thus, EPOR transcription and EpoR protein synthesis does not always lead to cell-surface expression of functional EpoR in tumour cells (Migliaccio et al, 1991; Neumann et al, 1993; Sawyer and Hankins, 1993; Hilton et al, 1995; Hermine et al, 1996; Kurten et al, 1996; Supino-Rosin et al, 1999). This evidence concerns the gene EPOR and neoplasm.