Pretreatment and midtreatment measurement of Oxygen tension levels in head and neck cancers

Objective: Considerable evidence exists to suggest that tumor hypoxia results in radioresistance. Historically, it has been difficult to assess tumor oxygen tension levels reliably. These levels can now be assessed in head and neck malignancies using the Eppendorf pO₂ histograph, which uses a fine-needle electrode and a computerized micromanipulator. This technology was used to compare the pretreatment tumor oxygen tension level in lymph node metastases of patients with head and neck cancer to measurements taken during nonsurgical treatment after a partial response had been achieved. Study Design: Prospective study. Methods: Oxygen tension levels were measured in the cervical lymph nodes of 10 patients with biopsy-proven head and neck squamous cell carcinoma and cervical metastases who were being treated with nonsurgical management. These levels were obtained using the Eppendorf pO₂ histograph system. Measurements were taken before the start of treatment and were repeated when the size of the cervical metastatic node had decreased by 50%. Normal subcutaneous tissue was measured during the same session. The mean and median pO₂ levels, as well as the percentage of measurements with pO₂ less than 5 mm Hg were determined. Results: A mean of 72.6 measurements per session was taken from each lymph node. The median tumor pO₂ measurement fell from a mean (±SD) of 13.9 ± 8.0 mm Hg to 7.3 ± 9.9 mm Hg. Even more dramatic, however, was the substantial increase in the percentage of values less than 5 mm Hg, a rise from 29% to 52%. Conclusions: While there is variability both in the pretreatment oxygenation of head and neck cervical metastases and in the change in tumor oxygen tension during treatment, there appears to be a decrease in the overall oxygenation of the tumors. The dramatic increase in very low oxygen measurements may reflect selective survival of radioresistant or chemoresistant hypoxic tumor cells. Cells at the very low level would be expected to be radiobiologically hypoxic (resistant to radiation-induced cell kill).