Survival Curves for Clonogenic Cells of a Murine Keratinizing Squamous Carcinoma Irradiated in Vivo or under Hypoxic Conditions

Summary

In its histological character and tendency to metastasize preferentially to lymph nodes, this tumour is indistinguishable from its clinical homologue. Of the morphologically intact cells released from the tumours by enzymatic treatment, 17 were required for 50 per cent successful transplantation to syngeneic hosts; this figure was reduced to 4 when a preponderance of radiation-killed cells was added to the inocula. The survival curve for cells of tumours irradiated in situ under hypoxic conditions gave D₀ = 340 R and n = about 2·0. The distribution of cell-survival values for tumours irradiated in vivo indicated that about 18 per cent of the viable tumour cells are hypoxic in vivo. Four out of five different stromated tumours for which similar data have been reported had between 15 and 21 per cent of their cells hypoxic in vivo. An attempt is made to explain these striking similarities in terms of a common micro-anatomical unit with dimensions referred to the limiting distance of diffusion of oxygen from a capillary into respiring tissue, as calculated by Thomlinson and Gray (1955).