Due to a dedifferentiation of tumor cells, some thyroid carcinomas lose their capability for radioiodine (RI) concentration. This phenomenon is associated with a worse prognosis and prevents effective treatment. Retinoic acid (RA) is known to induce redifferentiation in various kinds of tumors and has been used recently in thyroid cancer.
Methods: Twelve patients (9 women, 3 men) with 6 papillary, 4 follicular and 2 mixed-cell type tumors (including 4 Hurthle cell carcinomas) were treated orally with RA (dose: 1.18 +/- 0.37 mg/kg body weight) for at least 2 mo before RI therapy. None of the patients could be treated with any other modality (RI, surgery, external radiation) when RA administration was started. Initially, clinically important tumor sites did not take up significant amounts of RI. Changes of RI uptake and thyroglobulin (Tg) serum values were determined. Glucose metabolism was followed with fluorodeoxyglucose (FDG) PET imaging in 10 patients before and in 5 patients after RA treatment.
Results: In 2 patients, a significant RI uptake was induced by RA, and in another 3 patients a faint RI uptake was achieved (responder group). In 7 patients, no change of RI uptake was observed (nonresponder group). Median Tg was increased from 105-840 microg/liter during RA therapy in the responder group, which was significantly higher than the nonresponder group (173-134 microg/liter). FDG PET was positive in all 10 patients before RA therapy. PET showed variable patterns of changes (increase/decrease/disappearance) in glucose consumption related to RA response.
Conclusion: RA can induce RI uptake in some patients with RI negative thyroid carcinoma tumor sites. Response to RA is associated with a significantly higher increase of Tg, suggesting that a restoration of Tg synthesis can be addressed as a redifferentiation parameter in these patients.