Thyroid and Parathyroid Cancers

Cancers of the thyroid and parathyroid are rare tumors comprising <1% of all malignancies. However, the incidence of thyroid cancers, primarily well differentiated, is increasing globally attributed largely to overdiagnosis with the increasing use of imaging. Thyroid cancers present as enlargement of the gland (solitary/multiple nodules or diffuse enlargement) while parathyroid carcinomas are usually diagnosed biochemically with raised serum calcium. Fine-needle aspiration cytology and ultrasonography are the initial investigations that help establish diagnosis. Tumors must be triaged into well differentiated, medullary or anaplastic cancers which are distinct entities with different management guidelines. Cross-sectional imaging, positron emission tomography (PET) scan and tumor markers (calcitonin, thyroglobulin) are additional investigations that help plan treatment and follow-up. Surgery is the mainstay of treatment of these cancers and should aim to remove all gross tumor with minimum morbidity safeguarding the recurrent laryngeal nerve and parathyroids. Medullary cancers could be hereditary which must be diagnosed to rule out syndromic involvement of the adrenal and parathyroid glands. In addition, it helps to screen first-degree relatives who may carry the mutated gene. Anaplastic cancers are lethal and usually very advanced at the time of diagnosis with poor prognosis. Parathyroid carcinomas are difficult to diagnose but should be suspected by the presence of local, regional or distant metastases. Adjuvant treatment has a limited role with radiotherapy being used for specific indications. Differentiated thyroid cancers on the other hand are iodine avid, and radioiodine has important role in their management.