Changes in histology and cell kinetics during the growth course of xenografted squamous cell carcinoma.

Two xenografted tumor lines, established from squamous cell carcinomas of the head and neck, were studied with respect to the growth parameters of the Gompertz function and changes in growth rate, cell cycle phase distribution, and histologic pattern during the course of growth. The tumors were transplanted subcutaneously in the back. Both tumor lines exhibited growth curves compatible with Gompertzian growth. The parameters of the Gompertz function differed significantly between the tumor lines. Tumor volume doubling time also varied during the course of growth. Flow cytometric analysis of cell cycle phase distribution showed an initial decrease in the fraction of cells in S-phase, parallel with an increase in the fraction of cells in GO/1-phase. As much as 50% of the cells were mouse-derived in tumors less than 100 mm3 in volume, after which the proportion of mouse-derived cells decreased to below 10%. This variation correlated with changes in the histopathologic picture.