[Clinical value of the potential doubling time (Tpot) measured by flow cytometry]

The potential doubling time (Tpot) is defined as the time necessary to double the number of proliferating tumor cells in the absence of spontaneous cell loss. Tpot is thought to be a better index of tumor proliferation than clinically observed tumour volume doubling time. The in vivo measurement of Tpot is a possible way to detect fast growing tumours which would be better controlled by accelerated radiotherapy. The published data demonstrate the feasibility and the safety of the technique. Large variations in Tpot values were observed in tumors with similar histology, indicating an accelerated proliferation rate in some tumors. There are technical difficulties related to intra-tumor heterogeneity, sample contamination by normal cells, and inter-laboratory variability, which question the biological interpretation of Tpot. Further studies are ongoing to establish whether the in vivo measurement of Tpot 1) provides information that is independent of the "classical" prognostic factors, and 2) allows the early recognition of the patients likely to benefit from accelerated treatment.