FDG - a marker of tumour hypoxia? A comparison with [18F]fluoromisonidazole and pO2-polarography in metastatic head and neck cancer

Experimental data suggest that the accumulation of [18F]fluorodeoxyglucose (FDG) in malignant tumours is related to regional hypoxia. The aim of this study was to evaluate the clinical potential of FDG positron emission tomography (PET) to assess tumour hypoxia in comparison with [18F]fluoromisonidazole (FMISO) PET and pO2-polarography. Twenty-four patients with head and neck malignancies underwent FDG PET, FMISO PET, and pO2-polarography within 1 week. Parameters of pO2-polarography were the relative frequency of pO2 readings ≤2.5 mmHg, ≤5 mmHg and ≤10 mmHg, respectively, as well as the mean and median pO2. We observed a moderate correlation of the maximum standardised uptake value (SUV) of FDG with the tumour to blood ratio of FMISO at 2 h (R=0.53, p<0.05). However, SUV of FDG was similar in hypoxic and normoxic tumours as defined by pO2-polarography (6.9±3.2 vs 6.2±3.0, NS), and the FDG uptake was not correlated with the results of pO2-polarography. The retention of FMISO was significantly higher in hypoxic tumours than in normoxic tumours (tumour to muscle ratio at 2 h: 1.8±0.4 vs 1.4±0.1, p<0.05), and the FMISO tumour to muscle ratio showed a strong correlation with the frequency of pO2 readings ≤5 mmHg (R=0.80, p<0.001). These results support the hypothesis that tumour hypoxia has an effect on glucose metabolism. However, other factors affecting FDG uptake may be more predominant in chronic hypoxia, and thus FDG PET cannot reliably differentiate hypoxic from normoxic tumours. (orig.)