That's because the data -- from six studies and 225 patients -- showed that while a negative FDG-PET could rule out cancer, a positive test couldn't rule it in.
Up to a quarter of patients with thyroid nodules will have indeterminate aspirates, but only 20% to 30% of those individuals will have malignancies, the research team says in a March 22 online report in Cancer.
FDG-PET, or 18F-2-fluoro-deoxy-D-glucose positron emission tomography, has been suggested as a way to identify the patients who need surgery.
"The results of our meta-analysis suggest that for patients currently diagnosed with indeterminate thyroid nodules and in whom there is a strong contraindication against thyroidectomy, a negative FDG-PET may be helpful in the decision to postpone surgery in favor of a watchful waiting policy," lead author Dr. Dennis Vriens, from Radboud University Nijmegen Medical Center, told Reuters Health in an email.
While a negative result decreased the probability of malignancy to 3.6%, the pooled positive predictive value was only 38.7%.
FDG-PET had a pooled sensitivity of 94.8% (with moderate, nonsignificant inconsistency among studies) and a pooled specificity of 47.9% (with high, significant inconsistency between studies).
Its overall accuracy for confirming thyroid nodule malignancy was only 60%.
Three of 58 patients with differentiated thyroid carcinoma had false-negative FDG-PET scans. All three had particularly small lesions. FDG-PET had 100% sensitivity for detecting thyroid cancer in the 164 thyroid nodules that measured greater than 15 mm, although specificity remained only 46.6%.
"We performed this meta-analysis of available literature to evaluate whether or not it is worthwhile to design a multicenter trial, which will aid to definitively determine the role of FDG-PET in patients with indeterminate thyroid nodules," Dr. Vriens told Reuters Health.
Based on their findings, he and his colleagues conclude that "the incorporation of FDG-PET into the initial workup of such patients before surgery deserves further investigation."
"To adequately position FDG-PET in clinical care for these patients, we plan a multicenter study which will include patients with thyroid nodules, who are diagnosed as 'indeterminate' by ultrasonography guided fine-needle aspiration biopsy," Dr. Vriens said.
"These patients will receive an FDG-PET scan just before primary surgery. Blinded result from the PET will be compared to those of the pathology department. As it would be incorrect to refrain from surgery in patients who actually have thyroid cancer, we are especially interested in the fraction of patients in whom FDG-PET suggests benign disease, but surgery confirms malignancy (a fraction we expect to be very small based on our meta-analysis)."
By Will Boggs, MD
Last Updated: 2011-04-26 15:24:16 -0400 (Reuters Health)
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