Cell cycle time, growth fraction and cell loss in xenografted head and neck cancer.

: In a previous cell kinetic study with DNA flow cytometry (FCM) on xenografted human squamous cell carcinoma of the head and neck (HNSCC), there were significant variations in cell cycle phase distribution during early growth of the transplanted tumors. The object of the present study was to investigate further the cell kinetic mechanisms associated with variation in the growth rate of HNSCC. Xenografts from the same tumor line were examined on three different occasions: 12, 25 and 36 days following transplantation into nude mice. Cell cycle time "Tc", tumor growth fraction (GF) and cell loss factor were determined by computerized curve-fit analysis from percentage labelled mitoses curves. The mean growth curve of the tumors was logistic, with tumor doubling time (Td) ranging from 7.39 days to 8.86 days, and increasing as tumor volume increased. Although growth rate was higher in younger tumors, the cell cycle was longer with a median "Tc" of 69 hours on day 12 versus 34 hours on day 36. There were only minor variations in cell cycle phase distribution as measured by FCM. The growth fraction decreased slightly from 80% to 69% between day 12 and day 36, whereas cell loss factor increased markedly from 49% on day 12 to 78% on day 36. The results of the study emphasize the fact that cell loss is one of the most important cell kinetic determinants of tumor growth rate. This should be borne in mind when calculating proliferative cell kinetics in HNSCC.