Detection of cytokeratins 19/20 and guanylyl cyclase C in peripheral bloodof colorectal cancer patients

The clinical significance of detecting supposed tumour cell-derived mRNA tr anscripts in blood using the polymerase chain reaction (PCR) remains unclea r. We have used a fully quantitative 5'-nuclease RT-PCR assay to screen for the expression of cytokeratins (ck) 19 and 20 and guanylyl cyclase C (GCC) in the peripheral blood of 21 healthy controls and 27 colorectal cancer pa tients. Expression of cytokeratin 19 and 20 mRNA was detected in 30% and 10 0% of samples, respectively, taken from healthy volunteers. There was no ap parent difference in ck19 and ck20 mRNA transcription levels between contro ls and patients, or between patients with different Dukes' stages. While GC C mRNA was detected in only 1/21 control samples, it was expressed in appro ximately 80% of patients, although again there was no correlation between G CC levels and disease stage. Transcription levels of all three markers vari ed considerably between samples, even between samples taken from the same p erson at different times. We conclude that neither ck19 nor ck20 are reliab le markers for the detection of colon epithelial cells in peripheral blood and that an evaluation of the usefulness of GCC awaits further longitudinal studies.