Kinetic and Histological Changes of a Serially Transplanted Mouse Tumour

A serially transplanted mouse tumour, NT1, was studied histologically and by autoradiography using tritiated thymidine at three stages in its transplant history: after two, seventeen and twenty‐seven passages. the growth rate of the tumour decreased progressively with increasing passage number, and the mean cycle time of the tumour cells increased from 21 hr to 34 hr between the seventeenth and twenty‐seventh passages. Histologically the tumour changed from having an epithelial structure (second passage), to having a mixed structure with at least two histologically different regions (seventeenth passage), to having a fibrous structure (twenty‐seventh passage). Radiation response experiments were carried out on the second and twenty‐seventh passaged tumours, the results of which are consistent with the kinetic and histological changes.