Distant metastases of differentiated thyroid cancer: diagnosis, treatment and outcome.

The remarkably good prognosis and long-term survival in differentiated thyroid cancer (DTC) are significantly reduced in patients with distant metastasis (DM). Multi-site metastases are associated with a high mortality rate reaching 92% at 5 years necessitating early diagnosis and treatment. The most common site of metastases are the lungs, followed by the bone, with the former having better prognosis than the latter due to late detection. A number of factors contribute to the development of DM including large and multifocal primary tumour, extrathyroidal extension, aggressive histology and advanced age. In patients with good (131)I uptake, (131)I therapy appears highly effective and should be offered up to a cumulative activity of 22 GBq. Other measures such as surgery, radiotherapy, arterial embolisation and cementoplasty may be required. If there is low or no (131)I uptake, FDG-PET should be obtained due to its prognostic impact. It may help in selecting patients for other modalities such as cytotoxic chemotherapy and redifferentiation therapy by 13-cis retinoic acid. The development of tyrosine kinase inhibitors has raised hopes in providing alternative therapy for bone metastasis, especially in older age groups with poorly differentiated tumours with no (131)I uptake but good uptake of FDG.