An assessment of the reliability and reproducibility of measurement of potential doubling times (Tpot) in human colorectal cancers.

An assessment has been made of the reproducibility of measuring tumour proliferation using in vivo iododeoxyuridine (IUdR) labelling and flow cytometry. The variation that occurs between different institutions (Paterson Institute for Cancer Research, Manchester and the Gray Laboratory, Northwood), different observers and different runs on the same flow cytometer have been measured on 139 samples from 53 patients with colorectal cancer. The results demonstrate that the IUdR technique for measuring tumour proliferation is reproducible. Correlations were seen between measurements of Tpot obtained by different individuals and on separate machines. However, direct comparisons of the measured parameters showed that there were highly significant differences in the values obtained between institutes and observers (P < 0.001). Despite these variations, there were still significant detectable differences in Tpot measurements between individual tumours (P < 0.001). Analysis of the results obtained by running the same samples on two separate occasions on the same machine showed that the technique was highly reproducible and that the staining procedure was stable. Eighty per cent of the samples were similarly assigned to either above or below the median Tpot value, regardless which observer/laboratory combination was utilised. These data suggest that large clinical trials using Tpot should employ a single centre and a single individual to prepare, run and analyse samples.