Bexarotene increases uptake of radioiodide in metastases of differentiated thyroid carcinoma

Treatment options for metastases of differentiated thyroid carcinoma (DTC) are limited due to decreased uptake of radioiodide (I-131). Therefore, strategies to improve I-131 uptake are mandatory. It has been suggested that retinoids have beneficial effects on iodide uptake in vitro and in humans. However, to date, only studies with 13-cis-retinoic acid have been performed in humans. We therefore decided to study the effects of 6 weeks of treatment with the retinoid X receptor activator bexarotene on I-131 uptake in patients with metastatic DTC. Open prospective intervention study. Twelve patients with metastases of DTC, with insufficient uptake of I-131, received 6 weeks of treatment with 300 mg bexarotene/day. Prior to, and after this intervention, I-131 uptake was measured by whole-body scintigraphy and single photon emission tomography (SPECT) 3 days after 185 MBq I-131. Diagnostic imaging was preceded by two consecutive injections of recombinant human TSH. Bexarotene treatment induced I-131 uptake in metastases of 8 out of 11 patients (one patient died for reasons not related to the study). However, uptake was only discernable at SPECT and had incomplete matching with metastases as visualized by CT scanning. Bexarotene partially restores I-131 uptake in metastases of DTC. The clinical relevance of this observation may be limited due to the differential responses of the different metastases within each patient and the low intensity of I-131 uptake