Growth Characteristics of Human Melanoma Xenografts

The growth of twelve human malignant melanomas in athymic nude mice was studied. Gompertz curves were fitted to volumetric growth data. DNA histograms were obtained with flow cytometry. Each of the twelve melanomas exhibited a characteristic growth pattern, indicating that inherent properties of the tumours are important for the growth control. The theoretical maximum volumes (Vmax) ranged from 208 to 12,900 mm3, the volume doubling times (Td) from 2.8 to 15.3 days (V = 50 mm3) and from 3.8 to 64.6 days (V = 200 mm3), and the fraction of cells in S from 5 to 21%. Tumours with short Td were characterized by a higher growth fraction and probably by a lower cell loss factor than those with long Td. The growth was also influenced by the nude mouse host, as indicated by the values for Vmax, which were similar to those reported for mouse tumours (geometric mean = 8100 mm3), but considerably lower than the volumes of many tumours in man. Also the Td-values for the xenografts were generally lower than those reported for tumours in man, presumably due to a lower cell loss factor. During serial transplantation the growth rate of one of the melanomas increased abruptly, probably because of both an increased growth fraction and a reduced cell loss factor. The latter result demonstrates the necessity of keeping basic biological parameters of xenografts under observation during serial transplantation.