Clonogenic potential of human tumors. A hypothesis.

Conventional radiation therapy of medium-sized (2 to 5 cm diameter) squamous cell carcinomas of the head and neck has resulted in data which were pooled to produce a curve of local control versus dose. From this curve, estimates were made of the number of clonogenic cells in these tumors. These calculations demonstrate a much smaller number of clonogenic cells than is usually assumed for human tumors. It is postulated that a relatively small proportion of the cells in human tumors are clonogenic. The number of cells which need to be destroyed by radiation therapy or chemotherapy in order to produce tumor control may be much less than usually estimated.