Prognostic Value of [18F]Fluorodeoxyglucose Positron Emission Tomographic Scanning in Patients with Thyroid Cancer

Abstract

Poorly differentiated thyroid cancer lesions often lose the ability to concentrate radioactive [131I]iodine (RAI) and exhibit increased metabolic activity, as evidenced by enhanced glucose uptake. We incorporated [18F]fluorodeoxyglucose (FDG) positron emission tomography (PET) scanning into the routine follow-up of a cohort of thyroid cancer patients undergoing annual evaluations. One hundred and twenty-five patients who had previous thyroidectomies were included. They had diagnostic RAI whole body scans, serum thyroglobulin measurements, and additional imaging studies as clinically indicated. During 41 months of follow-up, 14 patients died. Univariate analysis demonstrated that survival was reduced in those with age over 45 yr, distant metastases, PET positivity, high rates of FDG uptake, and high volume of the FDG-avid disease (>125 mL). Survival did not correlate with gender, RAI uptake, initial histology, or grade. Multivariate analysis demonstrated that the single strongest predictor of survival was the volume of FDG-avid disease. The 3-yr survival probability of patients with FDG volumes of 125 mL or less was 0.96 (95% confidence interval, 0.91, 1.0) compared with 0.18 (95% confidence interval, 0.04, 0.85) in patients with FDG volume greater than 125 mL. Only 1 death (of leukemia) occurred in the PET-negative group (n = 66). Of the 10 patients with distant metastases and negative PET scans, all were alive and well. Patients over 45 yr with distant metastases that concentrate FDG are at the highest risk. Once distant metastases are discovered in patients with differentiated thyroid carcinoma, FDG-PET can identify high and low risk subsets. Subjects with a FDG volume greater than 125 mL have significantly reduced short term survival.

Management Guidelines for Patients with Thyroid Nodules and Differentiated Thyroid Cancer: The American Thyroid Association Guidelines Taskforce

“…In one study, administration of 200-300 mCi of radioiodine to 10 patients with pulmonary macrometastases who had negative 3 mCi diagnostic scans was associated with a fivefold increase in the median TSH-suppressed thyroglobulin, and death was reported in several patients within 4 years of treatment (256). Although not specifically limited to pulmonary lesions, patients with increasing volumes of 18-fluorodeoxyglucose (FDG)-avid disease seen on positron-emission tomograpy (PET) scans were less likely to respond to radioiodine and more likely to die during a 3-year follow-up compared with FDG-negative patients (257). One study found that radioiodine therapy of metastatic lesions that were positive on FDG-PET scanning was of no benefit (258).…”

Histopathologic characterization of radioactive iodine‐refractory fluorodeoxyglucose‐positron emission tomography‐positive thyroid carcinoma

“…10 The majority of patients referred for PET scanning had RAIR disease. A patient was deemed RAIR if the patient had an elevated serum thyroglobulin with structural disease in the setting of a negative radioiodine whole-body scan.…”

“…10 Briefly, patients were fasted for at least 6 hours before intravenous injection of 10 to 15 millicurie (mCi) (370-555 megabecquerel [MBq]) of FDG. When patients were imaged with a combined PET/ CT, the associated CT images were evaluated in the same planes for anatomic reference.…”

Prognostic implication of fluorine‐18 fluorodeoxyglucose positron emission tomography/computed tomography in patients with recurrent papillary thyroid cancer

“…24,25 During dedifferentiation, it was postulated that thyroid malignancies simultaneously become more avid for nutrients, particularly glucose. It then became clear that the high metabolic activity revealed by FDG avidity implied poorly differentiated elements.…”