Objective: There is continued investigation of agents capable of overcoming hypoxic cell radioresistance. The evaluation of tumor oxygenation, therefore, assumes great importance. Previous efforts to measure tumor oxygen tension (PO2) using polarographic methods were limited by the size of the electrodes and efficiency of measurements. A new system employing fine-needle electrodes and a computerized micromanipulator was evaluated.
Design: Prospective study.
Patients: Sixteen patients with cancers of the head and neck, seen at Stanford (Calif) University Medical Center and Santa Clara Valley Medical Center, San Jose, Calif, between March 1, 1991, and July 31, 1991. Of the 16 tumors, 14 were squamous cell carcinomas; 11 were previously untreated. In two patients, measurements were repeated during radiation therapy. In three patients, measurements were taken under conditions of varied inspired oxygen during anesthesia. In seven patients, subcutaneous tissue (SQ) measurements were made for comparison.
Results: The mean (+/- SD) PO2 of all tumors was 25.6 +/- 20.2 mm Hg, with a range of 2.3 to 76.4 mm Hg. When only squamous cell carcinomas were considered, the mean tumor PO2 was 22.7 +/- 16.0 mm Hg. The mean SQ measurement was 57.2 +/- 12.8 mm Hg. In all cases (seven of seven) in which SQ data were available, the tumor PO2 was lower than the SQ PO2 by an average of 41.8 mm Hg. The mean tumor PO2 increased in two of three cases of hyperoxia and decreased in the the third. The mean tumor PO2 increased in one patient after 25 Gy of radiotherapy and remained the same in the other.
Conclusions: These measurements suggest that there is significant interindividual variability in the PO2 of head and neck cancers. Squamous cell cancers are generally less well oxygenated than normal SQ tissue. The PO2 histograph identified patients with a low mean tumor PO2.