Purpose: Metastases of differentiated thyroid cancer (DTC) in sites different from lungs and bone are unusual (UM); their impact in management and prognosis remains unknown. Our aim was to evaluate the prevalence of UM, to describe their characteristics and to analyze their impact in disease outcome and mortality.
Methods: We retrospectively reviewed the file records from 8 different centers. Those patients with DTC and UM were included. UM were diagnosed by: (i) biopsy/cytology and/or (ii) radioiodine (RAI) uptake associated to elevated thyroglobulin (Tg) levels and/or c) presence of one or more structural lesion/s with 18-FDG uptake in the PET/CT scan and elevated Tg levels.
Results: Thirty-six (0.9%) out of a total of 3982 DTC patients were diagnosed with UM; 75% had papillary histology. The most frequent localization was central nervous system (CNS, 31%). UM were metachronous in 75%, symptomatic in 55.6% and fulfilled RAI-refractoriness criteria in 77.8% of cases. Metastatic lesions in lung/bone and/or locoregional disease were present in 34 cases (94.4%). Diagnosis of UM changed the therapeutic approach in 72.2% of patients. After a median follow up of 13 months, 21 (58.3%) patients died from DTC related causes. In 8 of them CNS progression was the immediate cause of death.
Conclusions: Prevalence of UM was low; they were frequently metachronic and RAI-refractory. Although UM were found in patients with widespread disease, their diagnosis usually led to changes in therapy. UM were associated with poor prognosis and high frequency of disease-specific mortality.
Keywords: Advanced thyroid cancer; Distant metastases; Radioiodine refractory; Thyroid carcinoma; Unusual metastases.