Combined therapy with ¹³¹I and retinoic acid in Korean patients with radioiodine-refractory papillary thyroid cancer

Purpose: The aim of this study was to assess the clinical outcome of redifferentiation therapy using retinoic acid (RA) in combination with 131I therapy, and to identify biological parameters that predict therapeutic response in Korean patients with radioiodine-refractory papillary thyroid carcinoma (PTC). Materials and methods: A total of 47 patients (13 men, 34 women;age 54.2±13.6 years) with radioiodine-refractory PTC underwent therapy consisting of consecutive treatment with ¹³¹I and RA. Each ¹³¹I/RA treatment cycle involved the administration of oral isotretinoin for 6 weeks at 1-1.5 mg/kg daily followed by a single oral dose of 131I (range 5.5-16.7 GBq). Therapeutic responses were determined using serum thyroglobulin (Tg) levels and the change in tumour size 6 months after completing the ¹³¹I/RA therapy. Biological parameters and pathological parameters before and after combined therapy were compared. Results: After completing ¹³¹I/RA therapy, 1 patient showed a complete response, 9 partial response, 9 stable disease, and 28 progressive disease, representing an overall response rate of 21.3%. Univariate analysis revealed thatan age of <45 years and a persistently high serum Tg level were related to a good response. No clinical response was achieved when metastases showing no iodine uptake were present. Multivariate regression analysis showed that an age of <45 years was significantly associated with a good response. Of the 24 patients with well-differentiated carcinoma, 5 (20.8%) responded to ¹³¹I/RA therapy, whereas all 6 patients with poorly differentiated carcinoma failed to respond. Conclusion: ¹³¹I/RA therapy was found to elicit a response rate of 21.3% among patients with radioiodine-refractory PTC, and an age of <45 years was found to be significantly associated with a good response.