Labelling index of human squamous cell carcinomas. Comparison of in vivo and in vitro labelling methods.

In vivo and in vitro labelling has been compared in sixteen human solid squamous cell carcinomas (ENT). The median in vivo/in vitro LI ratio was 1-2, but for two-thirds of the patients it was only 1-1, suggesting a slight LI underestimation in vitro. Two factors can possibly explain the divergences: heterogeneity from one biopsy to another in the same tumour, and lower mean grain count in the deep cell layers of the in vitro labelled tumour samples. Therefore, the fact we did not find a good agreement between in vivo and in vitro data for one-third of the tumours points out that one must be cautious in considering in vitro LI as a valid result for a given patient. However, even if the in vitro LI leads to a certain underestimate, it can provide useful data.