Another putative CEA splice variant involving novel splicing of exons 9, 10 and the intervening intron sequence has been detected in the peripheral blood of colon cancer patients by reverse transcription PCR [47] . However, sequences within the middle part of a 152 bp PCR product (base pairs 26-99) of the putative CEA isoform isolated from white blood cells did not match any part of the genomic sequence of CEA. Therefore, this PCR product more likely represents a PCR artifact and not a real CEA splice form. Consequently, we did not investigate this putative CEA splice variant further.