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

The aim of this study was to assess the clinical outcome of redifferentiation therapy using retinoic acid (RA) in combination with I-131 therapy, and to identify biological parameters that predict therapeutic response in Korean patients with radioiodine-refractory papillary thyroid carcinoma (PTC). 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 I-131 and RA. Each I-131/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 I-131 (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 I-131/RA therapy. Biological parameters and pathological parameters before and after combined therapy were compared. After completing I-131/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 that an 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 I-131/RA therapy, whereas all 6 patients with poorly differentiated carcinoma failed to respond. I-131/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.