Hypoxic fraction determinations with the BA1112 rat sarcoma: variation within and among assay techniques

Measurement of the hypoxic fraction in the same tumor system by different assay techniques often gives incompatible results. The hypoxic fraction of the BA1112 sarcoma has been measured by three assay techniques: tumor control and growth delay assays in which the tumors remain in situ after irradiation, and paired survival curve assays in which the tumors are excised after irradiation. The assays were done with and without anesthesia on tumors growing in two different subcutaneous sites. Anesthesia of the hosts produced a statistically significant decrease in the calculated hypoxic fraction in a tumor control assay, but not in a paired survival assay. The excision assays gave consistently higher hypoxic fraction estimates than either the tumor control or growth delay assays. Some of the factors which could produce higher hypoxic fractions in excision assays than in in situ assays are discussed. Interpretation of the results was complicated by disagreements between the growth delay and tumor control assays, and by disparities between replicate determinations. The discrepancies among assays are caused almost entirely by variations in the response of the artificially hypoxic tumors, rather than variations in the response of aerobic tumors. These results indicate that assumptions commonly made when measuring hypoxic fractions may not be valid.