Excellent Response after Radioiodine Therapy of a Bone Metastasis of Skull from Follicular Thyroid Carcinoma, Fifteen Years after the First Treatment

Bone is the second most frequent site of metastases from differentiated thyroid carcinoma (DTC). Bone metastases (BM) occurs in about 10% of all patients with DTC. They are more frequently observed in follicular thyroid carcinoma (FTC) (7-28%), than in thyroid papillary carcinoma (PTC) (1-7%) [1,2] and are associated to unfavorable clinical out-comes, mainly related to skeletal related events (SREs), such as pathologic fractures, bone pain, spinal cord compressions and hypercalcemia, which impair the quality of life and reduce life expectancy. BM from DTC require multimodal and comprehensive treatment, including radioiodine therapy (RAI), palliative treatment, surgical treatment, external beam radiation and target drug therapy. RAI is the first line treatment, but about two thirds of DTC patients with distant metastases are not definitively cured. This treatment is considered less effective in BM particularly in case of large metastases. The different response to RAI treatment alone or associated to BM focal treatment depends to RAI avidity of lesions [3]. We report the rare case of an excellent response to RAI of a metachronous bone metastasis of skull from FTC, in a 72 yrs old woman, diagnosed 15 years after the first treatment, followed by a complete regression of radioiodine up-taking area with persistence of excellent response to the treatment six years after it. This case confirms that the complete BM response to RAI treatment depends to the degree of dedifferentiation of cancers cells and enforce the concept of a long- life follow-up of FTC patients.