Thyroid cancer is the most common endocrine malignancy. It has the highest incidence in the United States and is increasing worldwide. In 2014, approximately 63,000 new cases of thyroid carcinoma were diagnosed in the United States, accounting for 4% of all new malignant disease. Three of four all new thyroid cancer diagnoses are made in women, corresponding to the threefold higher rates seen in women between 2007 and 2011 (1). Thyroid cancer occurs less frequently in children compared to adults, with a peak incidence of around 50 years. Despite this, overall long-term survival remains favorable (2). Histologic types (Table 43-1) include those that derive from the follicular epithelial cells (papillary and follicular), which account for the majority of thyroid cancers, and from the parafollicular C cells (medullary) (2). Other thyroid tumors, including primary lymphomas of the thyroid, which are usually metastases from other primary sites, are also encountered, although rarely.
Table 43-1Types of Thyroid Cancer ||Download (.pdf) Table 43-1 Types of Thyroid Cancer
|Type ||Frequency ||Prognosis (10-year overall survival) |
|Originating from follicular cells |
| Papillary ||80% ||93% |
| Follicular ||11% ||85% |
| Hürthle cell ||3% ||76% |
| Anaplastic (undifferentiated) ||2% ||14% |
|Originating from C cells |
| Medullary ||4% ||75% |
EVALUATION OF SOLITARY THYROID NODULES
Thyroid cancer usually presents as a nodule identified on physical examination or discovered incidentally on imaging studies performed for unrelated reasons. However, most thyroid nodules are benign, with about 10% to 15% found to be malignant on biopsy (3). The main diagnostic challenge is accurately differentiating benign from malignant disease in order to ensure appropriate definitive therapy and avoid unnecessary treatments.
Clinically palpable nodules are found in approximately 5% of the population (4). Benign and malignant nodules are almost always clinically indistinguishable. Features indicating increased likelihood of carcinoma are summarized in Table 43-2. Initial evaluation and management of patients presenting with thyroid nodules is detailed in Fig. 43-1.
Table 43-2Clinical Features Associated With Increased Risk of Malignancy ||Download (.pdf) Table 43-2 Clinical Features Associated With Increased Risk of Malignancy
Age <20 years
Presence of cervical lymphadenopathy
History of radiation to the head and neck during childhood
Family history of medullary thyroid cancer or MEN types 2A and 2B
Hard fixed nodule
Recent nodule growth
Hoarseness of voice (indicating invasion of recurrent laryngeal nerve)
Evaluation of thyroid nodules. FNA, fine-needle aspiration; TFT, thyroid function test; TSH, thyroid-stimulating hormone; US, ...