[F]-FDG-PET/CT and [F]-FAZA-PET/CT Hypoxia Imaging of Metastatic Thyroid Cancer: Association with Short-Term Progression After Radioiodine Therapy.

PURPOSE

To examine the relationships between 2-deoxy-2-[F]fluoro-D-glucose ([F]-FDG) and hypoxia tracer [F]fluoro-azomycinarabinofuranoside ([F]-FAZA) and between I and [F]-FAZA uptake in patients with metastatic thyroid cancer and to evaluate imaging features associated with short-term progression after I therapy.

PROCEDURES

The study population was 20 patients (17 women and 3 men; mean age, 67 years) with metastatic thyroid cancer who underwent both [F]-FDG- and [F]-FAZA-positron emission tomography (PET)/X-ray computed tomography (CT) examinations before I therapy. Short-term response to radioiodine was assessed (mean follow-up, 19 months ± 9). PET parameters including [F]-FDG-SUVmax, [F]-FAZA-SUVmax, and [F]-FAZA-tumor-to-muscle [T/M] were obtained. Mann-Whitney U, Wilcoxon signed-rank, or χ tests were used to assess differences between two quantitative variables or compare categorical data. Predictive factors for short-term progression were investigated with logistic regression analysis.

RESULTS

Eleven lymph node metastatic lesions were identified in 9 patients and 46 distant metastatic lesions (lung, 19; bone, 17; and liver, 10) in 14 patients. A total of 24 I-positive and 33 I-negative lesions were detected. SUVmax was significantly lower with [F]-FAZA-PET/CT (1.3 ± 0.6) than with [F]-FDG-PET/CT (6.4 ± 5.9, p < 0.001). No significant correlation was observed between [F]-FAZA-PET/CT and I imaging concerning visibility (p = 0.36). After I therapy, 31 of 57 metastatic lesions displayed short-term progression. Multivariate logistic regression revealed that [F]-FDG-SUVmax (p = 0.022) and [F]-FAZA-T/M (p = 0.002) showed significant associations with short-term progression.

CONCLUSIONS

Although [F]-FAZA uptake was low in metastatic thyroid cancers, not only glucose metabolism but also hypoxic conditions may be associated with progression after I therapy in patients with metastatic thyroid cancer.