Abstract
Fifteen xenograft tumour lines (4 osteosarcomas and 11 squamous carcinomas) were established on nude mice in numerous passages. Over a period of 4 years, samples were taken and studied systematically in more than 4000 histological slides. Of the tumour lines, 12 (4 osteosarcomas and 8 squamous carcinomas) showed remarkable dedifferentiation, but also redifferentiation towards a higher grade. There was a correlation between the rate of tumour takes in mice and poor prognosis in patients, but none between tumour doubling time and the phases of the cell cycle. Altogether, the results showed a great heterogeneity of human xenotransplants in terms of biological behaviour and morphological changes.