Irregular radiation response of a chondrosarcoma.

The DC II mouse chondrosarcoma is a potentially valuable radiobiological tumour system since it has been observed to recover from radiation injury by regrowth from clones that may be counted in histological sections. Unfortunately, the normal growth of this tumour following s.c. implantation in the thigh is irregular both in the time before growth becomes evident and in the rate of growth. The response to radiation is also unreliable since tumours irradiated with the same dose (e.g. 30 Gy) show a range of responses from shrinkage to no detectable change in growth rate. The delay in normal growth can be attributed largely to delays in vascularization while changes in growth rate may be explained by differences in tumour architecture. Radiation response may depend on variations in hypoxic fraction and in relative cellularity. Tumours having the same external dimensions may differ by a factor of 80 in the numbers of tumour cells they contain. This chondrosarcoma may prove a closer model to some human tumours than many transplantable tumours that display regular growth patterns.