Recovery from sublethal damage by acutely hypoxic tumour cells in vivo and in vitro.

The ability of acutely hypoxic tumour cells to recover from sublethal damage following irradiation in vivo and in vitro has been measured using a single tumour system. The methods of assay were tumour growth delay, local tumour control and tumour cell survival in vitro following treatment in vivo or in vitro. Tumours in vivo or cells in vitro rendered acutely hypoxic during irradiation were irradiated with either single doses or two doses 24 hours apart. Cells left in situ had a greater capacity for recovery than those treated either in vivo or in vitro and then assayed in vitro. It is suggested that tumours may not show a systematically reduced capacity for recovery relative to normal tissues, unless chronically hypoxic tumour cells have a reduced capacity for recovery and determine the response. However, the results imply that deductions as to the ability of tumour cells to recover from sublethal damage (whether chronically hypoxic or not), which rely on in vitro assays, may underestimate the extent of recovery.