Distant metastases from thyroid and parathyroid cancer.
Review
Overview
abstract
Thyroid cancer represents a unique biological tumor where even with the high incidence of distant metastases, the overall prognosis is not as poor as many other human cancers. The overall long-term survival in patients presenting initially with distant metastasis is approximately 50%. The overall incidence of distant metastases varies between 10 and 35%, depending upon the histology. The overall incidence is directly related to various histologies - being least in papillary thyroid carcinoma (10%) and highest in Hürthle cell tumor (33%). The incidence of distant metastases is also very high in patients with medullary and anaplastic thyroid cancer. The incidence of distant metastases at the time of initial presentation in differentiated thyroid cancer is approximately 4%. In high-risk patients - especially in patients with extrathyroidal extension or massive nodal metastasis - the distant metastases can be evaluated after total thyroidectomy with radioactive iodine ablation. Pulmonary metastases are very common in young individuals, but they are extremely well treated and the mortality from distant metastases in this group is very low. However, distant metastases in patients with poorly-differentiated carcinoma have a poor prognosis. In high-risk patients, generally a total thyroidectomy should be undertaken so that the patient can undergo radioactive iodine dosimetry and ablation as indicated. The surveillance in patients with thyroid cancer includes: close clinical follow-up, chest X-ray, and radioactive iodine dosimetry. Thyroglobulin is commonly used as a prognostic marker in patients having undergone total thyroidectomy. The incidence of distant metastases in medullary thyroid cancer is high, mainly to the lung and liver. Persistent hypercalcitonemia is an indication of regional or distant metastases. A variety of diagnostic tests are helpful, such as octreotide scanning, computed tomography scan, magnetic resonance imaging and positron emission tomography scan. Laparoscopy to evaluate the surface of the liver is also an important investigation to detect distant metastases. The incidence of distant metastases is very high in patients with anaplastic thyroid cancer, but most of the time the outcome depends on the locoregional recurrence and massive disease in the central compartment. The parathyroid cancer is quite rare, less than 1%, in patients undergoing parathyroidectomy. The diagnosis of parathyroid cancer is made by pathological features but the most certain method of diagnosis of a malignant tumor of the parathyroid is the identification of secondary deposits. The incidence of distant metastasis is difficult to determine due to the rarity of this condition, but the most common site is the lung. Patients with distant metastasis have recurrent progressive hypercalcemia along with high parathormone level.
