Pretreatment oxygenation predicts radiation response in advanced squamous cell carcinoma of the head and neck

Hypoxic tumor cells are known to be relatively radioresistant. The aim of the study was to correlate oxygenation status and radiation response in advanced squamous cell carcinomas of head and neck.

Pretreatment oxygenation status was measured in 34 lymph nodes and one primary tumor neck using oxygen electrodes. The primary oxygenation endpoint was the fraction of pO2 values less than 2.5 mmHg. Patients received standardized, conventional, external radiotherapy 66-68 Gy in 33-34 fractions.

Sixteen patients had loco-regional failure. Among these 16 patients the median of the fraction of pO2 values less than 2.5 mmHg was 22% (range 0-95%) as compared to 6% (range 0-51%) among patients with loco-regional tumor control. When separating all 35 patients by the median of the fraction of pO2 values less than 2.5 mmHg and comparing the 2 years actuarial tumor control probability using Kaplan-Meier estimates, the most hypoxic subgroup had significantly lower loco-regional tumor control (P = 0.013, Logrank test). By univariate regression analysis the fraction of pO2 values less than 2.5 mmHg was found to be significant as continuous variable (P = 0.010). Finally, by Cox multiple regression analysis the fraction of pO2 values less than 2.5 mmHg was found to be the strongest independent variable in predicting radiation response when using tumor control in the site of pO2 assessment as treatment endpoint (P = 0.018).

These results suggest that pretreatment tumor oxygenation status is predictive of radiation response, when using the fraction of pO2 values less than 2.5 mmHg as endpoint.