Thyroid cancer is the most common endocrine malignancy, with a rising global incidence. A structured evaluation of thyroid nodules is recommended for accurate diagnosis and management. A multidisciplinary approach with shared care between specialists and GPs ensures optimal care.
- The incidence of thyroid cancer is increasing worldwide.
- Structured assessment of a thyroid nodule consists of exclusion of hyperthyroidism, followed by neck ultrasonography and cytological examination of nodules that have a suspicious ultrasonographic appearance.
- Surgery (lobectomy or total thyroidectomy) is the first-line treatment of highly suspected or cytologically confirmed thyroid cancer.
- Adjuvant therapy, including radioactive iodine and thyroid-stimulating hormone suppression with levothyroxine therapy, is determined by evidence-based risk criteria.
- Dynamic staging and routine surveillance with thyroid ultrasound and measurement of thyroglobulin levels are important in the subsequent management of thyroid cancer.
- Optimal care involves multidisciplinary specialist management and a fully informed GP.
Picture credit: © Kateryna_Kon/stock.adobe.com
The global incidence of thyroid cancer is increasing and it is predicted to be the seventh most common cancer diagnosed in women in Australia in 2017.1 This is largely because of a greater number of incidental small cancers detected by neck imaging, as well as an increase in advanced stage papillary thyroid cancer (PTC).2
Thyroid cancers are a heterogeneous group of malignancies with a natural history that ranges from indolent to highly aggressive. People with thyroid cancer usually present with a thyroid nodule, but thyroid nodules are highly prevalent and mostly benign. A structured clinical approach is therefore important to identify at-risk patients, establish the diagnosis and plan management.
Classification and presentation
Thyroid cancer is classified according to cellular origin and degree of differentiation. Differentiated thyroid cancer arises from thyroid follicular epithelial cells and includes PTC, follicular thyroid cancer and poorly differentiated thyroid cancer usually of follicular thyroid cancer origin. These account for more than 95% of all thyroid cancers, and PTC accounts for about 90% of all differentiated thyroid cancers.3,4 Anaplastic thyroid cancer is a rare malignancy (<1% of thyroid cancers) that also arises from follicular cells and has a very aggressive clinical course.5 Medullary thyroid carcinoma arises from neural crest-derived parafollicular C cells, accounting for 1 to 2% of all thyroid cancers, and may occur as part of a genetic tumour syndrome (e.g. multiple endocrine neoplasia).6 Case finding of medullary thyroid carcinoma by measurement of serum calcitonin levels during nodule evaluation is not yet part of routine care.3 It is important to distinguish anaplastic thyroid cancer from primary thyroid lymphoma, which is a rare presentation of B-cell lymphoma usually occurring on the background of Hashimoto’s thyroiditis. This is managed similarly to lymphoma at other sites. This article will not discuss the management of anaplastic thyroid cancer, medullary thyroid carcinoma or thyroid lymphoma.
Clinically apparent thyroid nodules are present in 4 to 7% of the population but nodules detected on ultrasound are present in 17 to 68% of the population, with an incidence that increases with age.3 History and physical examination help to characterise suspicious features of thyroid nodules, including size and growth. However, most thyroid cancers are not diagnosed clinically unless the disease is advanced. Features of local invasion include hoarseness of voice (laryngeal nerve dysfunction), dysphagia, airway symptoms, haemoptysis, lymphadenopathy and fixation to surrounding tissue on examination. Known risk factors for thyroid cancer, including previous external beam radiation to the neck and familial thyroid cancer, are uncommon in the Australian community.3
Following detection of a thyroid nodule, levels of serum thyroid-stimulating hormone (TSH) should be measured to detect hyperthyroidism. If the TSH level is suppressed (TSH <0.01 mU/L), the nodule should be evaluated by radionuclide thyroid scanning for autonomy (a ‘hot’ nodule).3 Autonomously functioning nodules have an extremely low risk of malignancy and therapy should thereafter focus on treatment of hyperthyroidism. Routine measurement of serum thyroglobulin levels for initial evaluation of thyroid nodules is not recommended.3
Neck ultrasound should be performed for all thyroid nodules to confirm size and location, identify suspicious internal features and assess for cervical lymphadenopathy. These features help to guide further management (Table 1). The ultrasound findings with highest specificity for malignancy include microcalcifications, irregular margins and shape taller than wider on recumbent transverse view.3 Structured evidence-based systems such as the thyroid imaging and reporting data system are increasingly used to assist management decisions.7
For nodules considered to be sufficiently high-risk based on ultrasonographic features, fine needle biopsy is an accurate and cost-effective method of evaluation. The cytopathology is reported according to the Bethesda criteria to assist subsequent investigation and management (Table 2).3