Resistance of [¹⁸F]-Fluorodeoxyglucose-Avid Metastatic Thyroid Cancer Lesions to Treatment with High-Dose Radioactive Iodine

Abstract

Radioactive iodine (131I) is an important therapeutic option for the treatment of metastatic thyroid carcinoma. Survival in patients with metastases that concentrate radioiodine is better than those whose metastatic lesions do not take up radioiodine. Survival is markedly reduced in patients who have metastatic lesions that concentrate 18F-fluorodeoxyglucose (FDG) on positron emission tomography (PET). In this retrospective study, we evaluated the ability of 131I to destroy FDG-avid metastatic lesions in thyroid cancer patients. Twenty-five patients with positive FDG-PET scans received at least one dose of 131I treatment before a second FDG-PET was performed. The average interval between the two PET scans was 12.9 months. The average interval between the 131I treatment and the follow-up FDG-PET was 10.1 months. We measured posttherapy changes in lesional volume, in standard uptake values (SUV) of FDG, and in serum thyroglobulin (Tg) levels. The total volume of FDG-avid metastases rose significantly (p = 0.036) from a mean of 159 mL to 235 mL after 131I therapy, the maximum SUV rose from 9.3 to 11.9, the median Tg at the time of the second PET scan was 132% of that at baseline. Statistical analyses demonstrated no significant changes in maximum SUV, or serum Tg levels after 131I in the FDG-PET-positive group. In a control group of FDG-PET-negative patients, the serum Tg decreased to 38% of baseline after 131I therapy (p < 0.001). We conclude that high-dose 131I therapy appears to have little or no effect on the viability of metastatic FDG-avid thyroid cancer lesions.

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

“…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). In other studies of FDG-PET imaging, however, insufficient details exist in patients known to have pulmonary metastases to assess the utility of this modality to predict treatment response or prognosis (259).…”

“…This approach may identify the location of persistent disease in approximately 50% of patients (203,280) with a wide range of reported success. Some investigators have reported a decrease in serum thyroglobulin after empiric radioiodine therapy in patients with negative RxWBS (281,282), but there is no evidence for improved survival with empiric therapy in this setting (258,283). On the other hand, serum thyroglobulin levels may decline without specific therapy (282).…”

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

“…8 This change in biologic behavior has been attributed to the presence of poorly differentiated elements in the metastatic tumor of these patients. 9 However, to our knowledge, no study to date has been performed to examine the histology of FDG-PET-positive, RAI-refractory (RAIR) metastatic thyroid carcinomas.…”

FDG PET/CT in the Detection of Pancreatic Metastasis in a Patient with Follicular Thyroid Carcinoma and Negative I-131 Whole Body Scan Findings

“…Even high-dose I-131 therapy is quite ineffective in treating FDG-positive metastatic thyroid cancers. Therefore, in patients with Tg-positive and I-131-negative tumors, the complete surgical removal of iodine-negative lesions is the only curative treatment option (12).…”